Effects of streptozotocin and unilateral nephrectomy on L-type Ca2+ channels and membrane capacitance in arteriolar smooth muscle cells

Diabetes mellitus and hypertension are common diseases frequently coexisting. Although augmentation of L-type Ca2+ channel (I-CaL) activity has been reported in vascular smooth muscle cells (VSMCs) of a spontaneously hypertensive rat model, no study on I-CaL has been conducted for coexisting hypertension and diabetes. Sprague Dawley rats were assigned to four groups: a sham-operated control group (CG), a unilateral nephrectomy group (UNG), a streptozotocin (STZ)-induced type 1 diabetic group (SDG) and a coexisting hypertension and diabetes group (DHG), which underwent nephrectomy and received STZ injection. Blood pressure (BP) was significantly lower in the CG than in the other three groups. The membrane capacitance of VSMCs was nearly doubled in the SDG and DHG but not in the UNG. The I-CaL was increased approximately 2-fold in both the UNG and SDG and approximately 4-fold in the DHG. The current density of I-CaL was increased approximately 2-fold in the UNG and DHG, while no significant increase was seen in the SDG. The rate of Ca2+ removal was inhibited significantly, by similar to 33 %, in the DHG. In conclusion, the effects of hypertension and diabetes on I-CaL were apparently additive, and the vascular consequences of combined diabetes and hypertension may be caused by an elevated I-CaL and slowed Ca2+ removal.