Enhanced inhibition of L-type calcium currents by troglitazone in streptozotocin-induced diabetic rat cardiac ventricular myocytes.
1. Troglitazone, an insulin-sensitizing agent shown to improve cardiac function in both experimental animals and patients with diabetes, inhibits voltage-dependent L-type Ca(2+) currents (I(Ca,L)) in cardiac myocytes, which may underlie its cardioprotective effects. However, inhibition by troglitazone of I(Ca,L) in diabetic cardiac myocytes has not been characterized. 2. Using whole-cell voltage-clamp techniques, I(Ca,L) was measured in ventricular myocytes isolated from 4-6 weeks streptozotocin (STZ)-induced diabetic rats and age-matched control rats. 3. Under control conditions with CsCl internal solution, diabetic myocytes did not differ from control myocytes in membrane capacitance, current density or voltage-dependent properties of I(Ca,L). 4. Troglitazone decreased amplitude of I(Ca,L) in both control and diabetic myocytes in a concentration-dependent manner. This inhibition was more potent in diabetic than in control myocytes; half-maximum inhibitory concentrations of troglitazone measured at a holding potential of -50 mV were 4.3 and 9.5 micromol l(-1), respectively. 5. Troglitazone at 5 micromol l(-1) did not significantly influence the voltage dependency of steady-state inactivation or the inactivation time course of I(Ca,L) in either control or diabetic myocytes. 6. Since troglitazone inhibits I(Ca,L) more effectively in STZ-induced diabetic ventricular myocytes, this agent may prevent cardiac dysfunction in diabetes.
Department of Internal Medicine I, School of Medicine, Oita Medical University, Oita 879-5593, Japan.
Masaya
M
Arikawa
Naohiko
N
Takahashi
Tetsuya
T
Kira
Masahide
M
Hara
Tetsunori
T
Saikawa
Toshiie
T
Sakata
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D002839:Chromans / Q000494:pharmacology*; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013844:Thiazoles / Q000494:pharmacology*; D045162:Thiazolidinediones; D000077288:Troglitazone
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002839:Chromans; D007004:Hypoglycemic Agents; D013844:Thiazoles; D045162:Thiazolidinediones; D000077288:Troglitazone