muscle contraction is mediated by an elevation of cytosolic Ca2+ in
muscle contraction is mediated by an elevation of cytosolic Ca2+ in the ventricle that shows up partly from influx across the plasma membrane and mostly from sarcoplasmic reticulum release. 2002). The role that the exchanger plays in modulating normal heart function or in contributing to heart dysfunction in response to pathological disturbances on the other hand has been the Mouse monoclonal to GYS1 subject of much controversy (see several articles published in Lytton 2002). As can be gleaned from its name the LY2140023 Na+-Ca2+ exchanger operates by sequentially moving Na+ ions in one direction and Ca2+ ions in the other. Indeed the exchanger can operate in either direction depending upon the relative magnitude of the electrochemical gradients for Na+ and Ca2+. One of the most fundamental properties of this molecule then is the number of ions that bind and LY2140023 LY2140023 are subsequently transported the so-called stoichiometry of the exchanger. As operation from the Na+-Ca2+ exchanger generates a measurable current that moves in direction of Na+ transportation it is very clear that a lot more than two Na+ should be transported for every Ca2+ ion. But precisely 2000) utilized a cautious thermodynamic method of calculate how the stoichiometry from the Na+-Ca2+ exchanger assessed in areas torn faraway from guinea-pig cardiac myocytes was 4:1 an observation consequently corroborated utilizing a identical approach inside a recombinant program (Dong 2002). What’s the reason behind these disparate outcomes then? In today’s problem of (2002) make use of a stylish experimental method of provide a feasible explanation and by doing this swing the pounds from the pendulum back again toward 3:1. Using guinea-pig myocytes put through whole-cell patch-clamp these writers 1st reconfirm previously released observations demonstrating that procedure from the Na+-Ca2+ exchanger can itself alter ionic circumstances sufficiently to invalidate the thermodynamic strategy. Then within their crucial experiment they primarily inhibit the exchanger with Ni2+ under circumstances in which additional channels and pushes will also be inhibited and examine the reversal potential (a delicate thermodynamic parameter indicative of Na+-Ca2+ exchanger stoichiometry) as exchanger current builds up after Ni2+ washout. They discover that under circumstances where the exchanger can be poised to build up Ca2+ presuming LY2140023 a 3:1 stoichiometry (but ought to be near equilibrium to get a 4:1 stoichiometry) the assessed reversal potential shifts as time passes until a fresh equilibrium can be achieved. Alternatively under circumstances where in fact the exchanger can be initially poised near its equilibrium stage for a 3:1 stoichiometry (but should drive Ca2+ efflux if the stoichiometry is 4:1) the current that develops upon washout has a stationary reversal potential. These results are clearly consistent with a 3:1 but not a 4:1 stoichiometry. These findings raise the question: LY2140023 could erroneous assumptions regarding sub-membrane ionic conditions have confounded the earlier reports by Fujioka (2000) and Dong (2002) and thus accounted for the apparent measured stoichiometry of 4:1? This is the argument put forth by Hinata (2002). While it is hard to explicitly rule out such a scenario both of these studies included a series of careful controls which suggested but did not prove that control over submembrane ionic conditions was precise and accurate. Could the currents measured by Hinata (2002) have been contaminated with ionic conductances not related to the exchanger? The LY2140023 inhibitors they use to define Na+-Ca2+ exchange are not particularly selective and so while this is conceivable again a series of controls argues against such a possibility. Where does this leave us? Certainly a ‘counting of hands’ approach would lead one to conclude the Na+-Ca2+ exchanger stoichiometry is 3:1. And the current work of Hinata (2002) is beginning to shut the door on those outlying studies that still favour a 4:1 stoichiometry. Is there room for one more kick at the can before the crack is closed? Perhaps it would be possible to use a combination of Ca2+ flux measured by indicator dyes and whole-cell voltage-clamp to put the issue to rest at.