PREFERENTIAL REGULATION OF RABBIT CARDIAC L-TYPE CA2+ CURRENT BY GLYCOLYTIC DERIVED ATP VIA A DIRECT ALLOSTERIC PATHWAY

1. The activity of Ca2+ channels is regulated by a number of mechanism s including direct allosteric modulation by intracellular ATP. Since A TP derived from glycolysis is preferentially used for membrane functio n, we hypothesized that glycolytic ATP also preferentially regulates c ardiac L-type Ca2+ channels. 2. To test this hypothesis, peak L-type C a2+ currents (I-Ca) were measured in voltage-clamped rabbit cardiomyoc ytes during glycolytic inhibition (2-deoxyglucose + pyruvate), oxidati ve inhibition (cyanide + glucose) or both (full metabolic inhibition; FMI). 3. A 10 min period of FMI resulted in a 40.0% decrease in peak I -Ca at +10 mV (-5.1 +/- 0.6 versus -3.1 +/- 0.4 pA pF(-1); n = 5, P < 01). Similar decreases in peak I-Ca were observed during glycolytic in hibition using 2-deoxyglucose (-6.2 +/- 0.2 versus -3.7 +/- 0.2 pA pF( -1); n = 5, P < 0 01) or iodoacetamide (-6.7 +/- 0.3 versus -3.7 +/- 0 .2 pA pF(-1); n = 7, P < 0 01), but not following oxidative inhibition (-6.2 +/- 0.4 versus -6.4 +/- 0.3 pA pF(-1); n = 5, n.s). The reducti on in I-Ca following glycolytic inhibition was not mediated by phospha te sequestration by 2-deoxyglucose or changes in intracellular pH. 4. Reductions in I-Ca were still observed when inorganic phosphate and cr eatine were included in the pipette, confirming a critical role for gl ycolysis in I-Ca regulation. 5. with 5 mM MgATP in the pipette during FMI, peak I-Ca decreased by only 18.4% (-6.8 +/- 0.6 versus -5.5 +/- 0 .3 pA pF(-1); n = 4, P < 0.05), while inclusion of 5 mM MgAMP- PCP (be ta,gamma-methyleneadenosine 5'-triphosphate, Mg2+ salt) completely pre vented the decrease in peak I-Ca (-6.9 +/- 0.3 versus -6.5 +/- 0.3 pA pF(-1); n = 5, n.s.). 6. Together, these results: suggest that I-Ca is regulated by intracellular ATP derived from glycolysis and does not r equire hydrolysis of ATP. This regulation is expected to be energy con serving during periods of metabolic stress and myocardial ischaemia.