MECHANISM OF PRESERVATION OF MYOCARDIAL CALCIUM-CHANNEL FUNCTION BY PYRUVATE CARDIOPLEGIC SOLUTION

We evaluated the effects of adding pyruvate to a cardioplegic solution on the preservation of the dihydropyridine-sensitive calcium (Ca2+) c urrent responses to beta-adrenergic stimulation in rabbit cardiac myoc ytes by measurement of single-channel open probability, Single ventric ular myocytes were isolated and stored in St, Thomas' solution with or without pyruvate at 4 degrees C for 2, 6, 12, or 24 hours, and cell-a ttached single Ca2+ channel currents recordings were made at 20 degree s to 22 degrees C after each storage period, When 0.1 mu mol/L isoprot erenol (ISO) was applied to the cells, the percent mean open probabili ty of the Ca2+ channels tested in freshly isolated cells was 181% +/- 27% (n = 12) of control values. These responses decreased with an incr easing duration of the hypothermic storage and were only 112% +/- 22% (n = 5) of control values after 24 hours of storage in the absence of pyruvate, Conversely, the responses were significantly preserved, to a s much as 143% +/- 17% (n = 7), in the presence of 10 mmol/L pyruvate in the storage solution. The application of forskolin to stimulate ade nylate cyclase or a membrane-permeable cyclic adenosine monophosphate mimicked the effects of ISO when the myocytes were stored with pyruvat e, Pyruvate did not alter the open-channel kinetics or single-channel conductance and lacked any apparent direct effect on the Ca2+ channel activity, We suggest that pyruvate added to the hypothermic storage so lution preserves the high-energy phosphates in myocytes that are respo nsible for Ca2+ channel phosphorylation via p-adrenergic stimulation.