Abnormally expressed low-voltage-activated calcium channels in beta-cells from NOD mice and a related clonal cell line.
A macroscopic low-voltage-activated (LVA) inward current was found in pancreatic beta-cells isolated from NOD mice. However, this current was not present in nondiabetic prone mouse (e.g., Swiss-Webster) pancreatic beta-cells. We performed pharmacological analyses on this current in NOD insulinoma tumor cells (NIT-1). This cell line was developed from pancreatic beta-cells of a transgenic NOD mouse. The sodium-channel blocker, tetrodotoxin (TTX; 2 micromol/l) had no effect on this LVA current. The amplitudes of currents elicited by a -20 mV test pulse retained similarity when the extracellular sodium concentration was increased from 0 to 115 mmol/l; when the extracellular calcium concentration was decreased from 10 to 2 mmol/l, there was an approximate 50% reduction of this current elicited by a -30 mV test pulse. Neither the L-type calcium-channel blocker, nifedipine (3 micromol/l), nor the N-type calcium-channel blocker, omega-CgTx-GVIA (1 micromol/l), at -30 mV produced an appreciable effect. The T-type calcium-channel blockers, nickel (3 micromol/l) and amiloride (250 micromol/l), effectively reduced the peak of this current. In 2 mmol/l calcium external solution, the threshold of voltage-dependent activation of this calcium current was approximately -65 mV, and the peak current occurred at -20 mV. Half-maximum steady-state inactivation was around -43 mV. The mean time constant of slow deactivating tail currents generated by a preceding 20 mV pulse was 2.53 ms. The intracellular free calcium concentration was two- to threefold higher in NOD mouse pancreatic beta-cells compared with Swiss-Webster pancreatic beta-cells. We concluded that there are LVA calcium channels abnormally expressed in NOD mouse beta-cells. This LVA calcium channel may be factorial to the high cytosolic free calcium concentration observed in these cells, and thereby may contribute to the pathogenesis of NOD mouse beta-cells.
Wang
L
L
Department of Pharmacology, University of South Alabama, College of Medicine, Mobile 36688, USA.
Bhattacharjee
A
A
Fu
J
J
Li
M
M
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002460:Cell Line; D002999:Clone Cells; D004553:Electric Conductivity; D007340:Insulinoma / Q000503:physiopathology; D007515:Islets of Langerhans / Q000737:chemistry / Q000502:physiology*; D051379:Mice; D016688:Mice, Inbred NOD; D008822:Mice, Transgenic; D009532:Nickel / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D010190:Pancreatic Neoplasms / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D013779:Tetrodotoxin; D000584:Amiloride; D009532:Nickel; D020866:omega-Conotoxin GVIA; D012964:Sodium; D009543:Nifedipine