Na-Ca exchange current in mammalian heart cells

Abstract

Electrogenic Na-Ca exchange has been known to act in the cardiac sarcolemma as a major mechanism for extruding Ca ions. Ionic flux measurements in cardiac vesicles have recently suggested that the exchange ratio is probably 3 Na:1 Ca, although a membrane current generated by such a process has not been isolated. Using the intracellular perfusion technique combined with the whole-cell voltage clamp, we were able to load Na+ inside and Ca2+ outside the single ventricular cells of the guinea pig and have succeeded in recording an outward Na-Ca exchange current while blocking most other membrane currents. The current is voltage-dependent, blocked by La3+ and does not develop in the absence of intracellular free Ca2+. This report presents the first direct measurement of the cardiac Na-Ca exchange current, and should facilitate the study of Ca2+ fluxes during cardiac activity, together with various electrical changes attributable to the Na-Ca exchange and the testing of proposed models.

Cholinergic receptors regulate a voltage‐insensitive but Na+‐dependent calcium influx pathway in salivary acinar cells

“…Secondly Na+/H+ exchange will be blocked. This could result in an intracellular acidification in the resting cells and/or prevent the intracellular alkalinization that is reported during secretory stimulation 1141, It is possible that the calcium influx in salivary acinar cells is regulated by either [Na+]i or [H+], (see [15,16]). …”

Functionally distinct phospho-forms underlie incremental activation of protein kinase-regulated Cl- conductance in mammalian heart.

“…Omission of external K + and internal Na + also prevented currents generated by the Na+/K + pump (Gadsby and Nakao, 1989). Na+/Ca 2+ exchange current (Kimura, Noma, and Irisawa, 1986) was prevented by lack of internal Na + and internal and external Ca 2÷.…”

Alterations in [Ca2+]i mediated by sodium‐calcium exchange in smooth muscle cells isolated from the guinea‐pig ureter.

“…The advent of the whole-cell patch clamp technique has been instrumental recently in advancing our understanding of Na+-Ca2+ exchange in heart cells (Hume & Uehara, 1986;Kimura, Noma, & Irisawa, 1986;Mechmann & Pott, 1986). The advantage of this approach is that it is possible to measure in great detail the kinetics of the exchange-generated current, while controlling the electrochemical gradients of Na+ and Ca2+ with some degree of confidence (Kimura, Miyamae & Noma, 1987;Lipp & Pott, 1988).…”