CALCIUM CURRENT IN RAT DIABETIC VENTRICULAR MYOCYTES

The magnitude and kinetics of the L-type calcium current were compared in single left ventricular myocytes isolated from 8-mo-old (8M) and 1 9-mo-old (19M) genetically diabetic rats (WBN/Kob rats) and age-matche d control rats. A diabetic state occurred at 19M but not at 8M. The le ft ventricular contractility was reduced in 19M WBN/Kob rats compared with age-matched control rats. The duration of the action potential wa s longer in 19M WBN/Kob rats than in the age-matched control rats. Pea k inward current density was similar between diabetic rats and age-mat ched control rats. In addition, aging did not affect the current densi ty at 8M or 19M. The various kinetic parameters of the L-type calcium current were not different between 19M diabetic and control cell types . The percent increase in the amplitude of the calcium current induced by isoproterenol was less in diabetic cells at the age of 19M, but no t at the age of 8M, compared with age-matched control cells. Forskolin (10(-5) M), intracellularly applied adenosine 3',5'-cyclic monophosph ate (5 x 10(-5) M), and guanosine 5'-[gamma-thio]triphosphate (10(-4) M) were equally effective in increasing the current in 19M diabetic an d age-matched control cell types. The present study demonstrates that the basal calcium current density and kinetic parameters of the curren t were not altered. However, a decrease in response to beta-stimulatio n occurred in genetically diabetic rats compared with control rats.