Increased glucose tolerance in N-type Ca2+ channel alpha(1B)-subunit gene-deficient mice.

The voltage-dependent N-type Ca2+ channel is localized in the plasma membrane of insulin-releasing beta-cells and glucagon-releasing alpha-cells in the islets of Langerhans in the pancreas. To examine the contribution of N-type Ca2+ channel to glucose homeostasis, we performed glucose tolerance and insulin tolerance tests with N-type Ca2+ channel alpha(1B)-subunit-deficient mice on a normal or high-fat diet. The fasting glucose level in homozygous mice on the normal diet was significantly lower than those in wild and heterozygous mice. In glucose tolerance tests, the homozygous mice showed a higher glucose clearance rate and a similar pattern of insulin levels to those of wild and heterozygous mice. In insulin tolerance tests, glucose clearance rates showed no significant difference among wild, heterozygous and homozygous mice. In animals on the high-fat diet, food consumption was the same among wild, heterozygous and homozygous mice, but body weight gain was reduced in homozygous mice. After 8 weeks of the high-fat diet, homozygous mice showed lower fasting glucose levels and exhibited higher glucose clearance and lower insulin levels than wild or heterozygous mice in glucose tolerance tests. Glucose clearance rates showed no significant difference among wild, heterozygous and homozygous mice in insulin tolerance tests. After 10 weeks of the high-fat diet, the alpha(1B)-deficient homozygous mice showed lower lipid deposition in liver and lower plasma glucagon, leptin and triglyceride levels than wild or heterozygous mice. These results suggest that N-type Ca2+ channels play a role in insulin and glucagon release, and that N-type Ca2+ channel alpha(1B)-subunit deficient mice show improved glucose tolerance without any change in insulin sensitivity. Thus, N-type Ca2+ channel blockers might be candidate anti-diabetic/anti-obesity agents.