Altered L-type Ca2+ channel currents in vascular smooth muscle cells from diabetic rats

In spite of the presence of vascular complications of diabetes, alterations in Ca2+ channels in vascular smooth muscle cells (SMCs) from diabetic subjects have been unknown. In the present study, the whole-cell patch-clamp technique was used to examine L-type Ca2+ channels in tail artery SMCs from non-diabetic or diabetic rats, it was found that the densities of L-type Ca2+ channel currents at +20 mV were reduced from 4.5±0.6 pA/pF in non-diabetic rats (n=20) to 3.1±0.3 pA/pF in 2 month diabetic rats (n=20, p<0.05). The inactivation kinetics of L channel currents was also accelerated in tail artery SMCs as the diabetes status of the rats progressed. The exponential time constants of the current decay at +20 mV were 77.0±6.7 ms in non-diabetic rats (n=16) and 54.7±4.0 ms in 2 month diabetic rats (n=22, p<0.01). In contrast, the current-voltage relationships of L-type Ca2+ channels did not change in diabetes. The steady-state inactivation of the Ca2+ channels in diabetic rats also did not differ from that in non-diabetic rats. The present study demonstrates that the L channel density and the time course of inactivation of the current were altered in tail artery SMCs of diabetic rats. The decreased activity of voltage-dependent L-type Ca2+ channels in arterial SMCs from diabetic rats may be related to the development of certain vascular complications of experimental diabetes.