Studies of cellular correlates of ischaemia cardioprotection and KATP channel function in rat isolated ventricular cells
Hearts from female animals have been reported to be more resistant to ischaemia than those from males. Using rat isolated cardiac myocytes, I investigated gender differences in ischaemic resistance and whether it could be correlated with increased ATP-sensitive K+ (KATP) current density. Cells from female animals showed greater resistance to simulated ischaemia and reperfusion measured by an increase in the proportion of cells that recovered contractile function in response to stimulation and a reduction the number of hypercontracted cells. Female cells also had a greater ability to maintain calcium homeostasis in response to ischaemic challenge.;To measure KATP current density, whole-cell KATP currents were measured using patch clamp and normalised to cell capacitance. The KATP openers pinacidil or P-1075 elicited a higher KATP current density in female myocytes. However currents elicited by metabolic inhibition (NaCN + iodoacetate) were much larger than those produced by openers, and did not differ between genders. Similarly in cell-attached patch experiments there was no difference in the number of channels observed or their time to activation.;I also investigated the possibility, proposed recently, that protein kinase C may lead to internalisation of the KATP channel. In response to metabolic inhibition, whole-cell KATP currents are activated and then decline with time. Pre-incubation of myocytes with phorbol myristate acetate (PMA) did not affect the time course of the decline in contrast to the PKC inhibitor chelerythrine. Further, in cell attached patches, the single-channel open probability declined in the same way as did whole cell current, suggesting that the decline of whole-cell current reflects a fall in open probability rather than channel internalisation.