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 Ca(2+) channel (ICaL) activity has been reported in vascular smooth muscle cells (VSMCs) of a spontaneously hypertensive rat model, no study on ICaL 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 ICaL was increased approximately 2-fold in both the UNG and SDG and approximately 4-fold in the DHG. The current density of ICaL was increased approximately 2-fold in the UNG and DHG, while no significant increase was seen in the SDG. The rate of Ca(2+) removal was inhibited significantly, by ~33 %, in the DHG. In conclusion, the effects of hypertension and diabetes on ICaL were apparently additive, and the vascular consequences of combined diabetes and hypertension may be caused by an elevated ICaL and slowed Ca(2+) removal.