In guinea-pigs ventricular myocytes from female animals have been reported to have higher K_ATP current density than those from males, and also to show higher levels of mRNA for SUR2A estimated by RT-PCR¹. Further, female cells showed less Ca²⁺ loading in response to simulated ischaemia and reperfusion¹. We have investigated whether similar gender differences in tolerance to metabolic stress and cardiac K_ATP current density exist in the rat. Ventricular myocytes were isolated enzymatically from humanely killed adult rats. Cellular responses to metabolic stress and reperfusion were assessed by exposing cells to 7 min of metabolic inhibition (MI) with 2 mM CN^–and 1mM iodoacetate followed by 10 min reperfusion with normal Tyrode. Cells were field stimulated at 1 Hz throughout, fura-2 was used to measure [Ca²⁺]_i and contractile recovery was measured with a video-imaging system. [Ca²⁺]_i after 10 min reperfusion was higher in male than female myocytes (232 ± 14 nM vs 170 ± 8 nM, mean ± S.E.M. n=109 and 100 cells respectively, p<0.01, Students t test). Further, the percentage of female cells that had recovered the ability to contract in response to field stimulation 10 min after reperfusion was higher than that of male cells (74 ± 7% vs 42 ± 9%, n = 18,16 experiments respectively, p<0.05). Whole-cell K_ATP currents were measured using patch clamp in isolated male and female rat ventricular myocytes in response to MI, and normalised to cell capacitance. There was no significant difference between the maximal K_ATPcurrent density induced in male and female cells by MI (29.82 ± 2.91 pA/pF and 26.83 ± 1.79 pA/pF respectively, n = 27 and 24 cells respectively, 3 animals in each case). Single channel recordings from patches on cells exposed to MI indicated that neither the single channel conductance nor the time to K_ATP channel activation during MI differed between male and female myocytes. Transcript levels of genes encoding cardiac K_ATP channel subunits were estimated using quantitative PCR. These experiments failed to show any difference between male and female rats in the transcript level of genes encoding Kir6.2 or SUR2A. Thus although we found increased resistance to metabolic stress in cardiac myocytes from female rats, we did not find differences in K_ATP channel activity during MI, nor in transcript levels for Kir6.2 or SUR2A. This suggests that gender differences in stress resistance may be unrelated to K_ATP channel activity, or may result from differences in the pattern of channel activation that were not revealed by our experiments.