Cardiac Muscle Excitation Contraction Mediated From Sarcoplasmic Reticulum Biology Essay

Cardiac Muscle Excitation Contraction Mediated From Sarcoplasmic Reticulum Biology Essay In cardiac muscle, excitation-contraction coupling is mediated by calcium-induced calcium release from the sarcoplasmic reticulum through ryanodine receptors that are activated by calcium entry through L-type calcium channels on the sarcolemmal membrane. Although Ca2+ induced Ca2+ release triggered by the L-typed calcium current is the primary pathway for triggering Ca2+ from the sarcoplasmic reticulum, there are many other mechanisms that can also activate Ca2 + release from the sarcoplasmic reticulum such as Calcium induced calcium release (CICR) induced by T-typed calcium current, CICR triggered by calcium influx through Na+/Ca2+ exchange, and CICR mediated by calcium through tetrodotoxin (TTX)-sensitive Ca2+ current (ICa,TTX). As calcium is an important second messenger which is essential in regulating cardiac electrical activity as well as being the main activator of the myofilaments to which cause cardiac contraction. Mishandling of calcium is thought to lead many pathophysiol ogical conditions.  Knowledge of the mechanisms involved in regulating intracellular calcium and therefore contraction of the heart, may help to prevent and/or treat pathological conditions such as cardiac hypertrophy, arrhythmias or heart failure by using therapeutic agents targeted at modulating intracellular calcium. LIST OF FIGURES Figure 1: Calcium transport in ventricular myocytes 3 Figure 2: Six possible mechanism of cardiac excitation-contraction coupling 9 LIST OF ABBREVIATIONS LTCC = L-type calcium channels CICR = Calcium induced calcium release ECC = Excitation-contraction coupling NCX = Sodium-Calcium Exchange SR = Sarcoplasmic Recticulum ICa = Calcium current ICa,T = T-type calcium current ICa,L = L-type calcium current ICa,TTX = Tetrodotoxin-sensitive calcium current RyRs = Ryanodine Receptor [Ca2+]i = Intracellular calcium concentration [Ca2+]Tot = Total concentration of Calcium PKA = Protein Kinase A LVH = Left Ventricular Hypertrophy HOCM = Hypertrophic obstructiv e cardiomyopathy Introduction In heart muscle cell, the depolarization of action potential is due to the entering of Na+ ions via voltage gated Na+ channels and it is called fast inward current. The immediate repolarization is not possible due to rapidly inactivation of Na+ channel and initial depolarization allow the entering of calcium through voltage-grated Ca2+ channels and it is called second or the slow inward current. The rate of sodium channels inactivation is more rapid than that of calcium channels so that Ca2+ enters into the cell providing the membrane potential to close to 0mV for some part of action potential of heart muscle (Reuter, 1984). Excitation-contraction coupling (ECC) is the process in which an action potential triggers a myocyte to contract. In excitable muscle cells, the excitation signal causes rapid depolarization that produces the physiological response of contraction. Calcium is a ubiquitous second messenger, important in both, regulating the electrical activity of the heart as well as stimulating the myofilaments directly to cause contraction (Bers, 2001). In mammalian cardiac myocytes, the process of ECC is mediated by Ca2+ influx from the extracellular space that triggers Ca2+ Calcium – induced Calcium release (CICR) from the sarcoplasmic reticulum (SR) (Bers, 1991; Stern & Lakatta, 1992). When action potential reaches the myocyte, causing it to undergo depolarization, which causes calcium ions to enter the cell through L type calcium channel located on the sarcolemma and thereby trigger calcium release from the SR. Calcium influx and the intracellular calcium concentration trigger the contraction of heart due to binding of Ca2+ to cardiac muscle fiber protein, troponin C. For activation of SR calcium release, the L-type calcium current is the most widely accepted mechanism thought to be responsible for CICR. However, SR calcium release can also be triggered by calcium influx through sodium-calcium exchange, calcium infl ux via T-type Ca2+ current or through tetrodotoxin-sensitive Ca2+ current, or Inositol (1,4,5)-triphosphate (but not so much in cardiac muscle). Declining of calcium level in the cells cause the detachment of calcium from myofilament and resulting in relaxation of the heart. There are four main pathways for Ca2+ transport out of the cytosol including SR Ca2+ ATPase, sarcolemmal Ca2+-ATPase or mitochondrial Ca2+ uniport and sarcolemmal Na+/Ca2+ exchange. (Bers, 2002).

GM ignition switch recall Research Paper Example | Topics and Well Written Essays - 1000 words

GM ignition switch recall - Research Paper Example The deaths were linked to the failure of the airbags deployment during the accidents. However, reports suggested that an addition 72 persons died because of ignition key switch faults. Because of the faults, GM recalled over 29 million cars. In addition, the manufacturer incurred approximately $1.2 billion to counter the ongoing recalls and legal expenses (Cheeseman, 56). Various scholars have criticized the moral ethics exhibited by the GM management as their actions resulted in deaths and losses for the company. Ethics is a branch of philosophy that deals with ideas concerning what amounts to good and bad behavior. Based on the definition of ethics, it is clear that GM were ethically wrong since the management were aware of the faults in the vehicles long before they decided to recall. The management aim was to maximize the company’s profit rather than meet the customer needs. GM would have carried substantial tests of their vehicles before sale or in addition review the customer feedback concerning the vehicles. The company continued with the vehicle sales for more than seven years hence making then ethically liable. GM focused on the numbers of individuals who continued to enjoy problem free ignition related ignitions rather the ones who felt victim to the problem. Therefore, it has clearly to indicate that GM was ethically wrong. Socrates held being ethical as one of his primary role in all of his psychological theories. In addition, he held the belief that the suitable way for people to live was to aim at self-development rather than material wealth (Barry, 66). At all times, Socrates welcomed others individuals to attempt and focus more on a sense of friendships and real community since he had a sentiment that it was the suitable way for people to develop mutually as a populace. Socrates lived up to this doctrine and that is can be proved by his actions when he was

Information Searches Term Paper Example | Topics and Well Written Essays - 1000 words

Information Searches - Term Paper Example A low involvement product can also be one that requires less effort in decision making because it is constantly bought. A regular buying behavior normally occurs if the involvement is low and there is a small brand difference. (Sandhusen, 2000) In this case therefore, the consumer of the product selects it because it is familiar to him or her. A man’s perfume is a good example of a product in this category. Medium involvement purchase is defined as a situation whereby the consumer would not care when selecting a product for purchase. For instance when booking a holiday hotel room, the consumer may not mind about the nature of services at the hotel because he or she there for a short time. Most products and services in this category are normally impulse because there is normally no prior consideration to buy them. An example is the purchase of new dresses, blouse and jewelry for a night out. High involvement purchases are those whereby the buyer spares much time and effort in s earching for the products. Involvement in any type of purchase gets high for those products that are costly and are much significant to ones’ life. (Evans, 1982). Consumer behavior is the study of individual or groups and how they choose, secure and dispose products and services in order for them to get satisfied. ... (Kotler,1986). Consumers normally carry out both internal and external search. Internal search is normally a psychological process that involves a buyer’s perception about a certain product. The consumer may want to know about their direct experiences about a certain product in the market: The feelings, attitudes, beliefs and behaviors about a certain product in the market. For instance, a lady may not want to use certain soap because it dries her skin. Information search is also a tool to determine consumer behavior which is affected by the buyer’s learning, attitude, perceptions and risk.(Kotler,1986). Manufacturers of products will normally come up with the necessary actions which make consumers search for information about their purchases. These include processes such as, standardization of prizes for the products, advertising which creates awareness to customers for them to make the appropriate decision about a product. Again, they can offer promotions and free sam ples in order to motivate the buyers. Thirdly, manufacturing companies of these products should at times brand their products so that the customers can notice something new about the products and buy them. In the production of a lady’s perfume for instance, makers need to pay attention to the above marketing strategies. (Kotler,1986). Problem recognition helps consumers feel a discrepancy about the number of brands of a product in the market. The principles regarding problem recognition and reaching the consumer’s desired state include the following. First is the issue of product analysis. This is whereby makers of products look keenly in to the product before selling it to consumers. Again, the makers need to