Calcium and delayed potassium currents in mouse pancreatic beta‐cells under voltage‐clamp conditions.

Abstract

SUMMARY1. Pancreatic islets of NMRI mice were dissociated into single cells which were kept in tissue culture for 1-3 days. The whole-cell configuration of the patch-clamp technique was used to study inward and delayed outward currents of fl-cells under voltage-clamp conditions at 20-22 'C.2. Outward currents were suppressed by substituting the impermeant cation N-methyl-D-glucamine for intracellular K+. The remaining inward current had a V-shaped current-voltage relation reaching a peak value of 39 + 4 pA (mean + S.E. of mean) around -15 mV. It was identified as a Ca2+ current, because the peak amplitude was increased 1-6 times by increasing external [Ca2+] ([Ca2+]O) from 2-6 mm to 10 mM and it was blocked by Co2+ (5 mm) or nifedipine (5 gM) but not by TTX (20 /IM).3. The activation time constant of the inward current at -10 mV was 1P28 + 0-08 ms. The relation between the degree of activation (estimated from the size of the tail currents) and membrane potential V followed the sigmoidal function f =1/{1 + exp [(Vh -V)/k]} with half-maximal activation potential, Vh = 4+1 mV and slope factor, k = 14±+1 mV (for [Ca2+]o 10 mM).4. The inward current inactivated only weakly during depolarizing pulses of 0-1 -1 s duration. The delayed outward current (in experiments with 155 mm-internal [K+] ([K+]i))had a linear voltage dependence at potentials above -20 mV; its amplitude at -10 mV was 210 + 30 pA. Tail currents related to the activation of the outward current had K+-dependent reversal potentials. The current was blocked by extracellularly applied tetraethylammonium (20 mm) and 4-aminopyridine (2 mM). It was not affected by glibenclamide (3 /M), tolbutamide (0-2 mM) and alterations of intracellular [Ca2+] (1 nM-1 /tM). 6. The activation time constant of the outward current at -10 mV was 21 + 3 ms. The voltage dependence of activation could be described by the sigmoidal function (see above) with Vh = 19 + 1 mV and k = 5-6+0 4 mV.

‘Perforated patch recording’ allows long‐term monitoring of metabolite‐induced electrical activity and voltage‐dependent Ca2+ currents in pancreatic islet B cells

“…Similar results were obtained while recording from human islet cells in clumps. These currents resemble whole-cell Ca2+ currents previously reported in rodent B cells [2,8] whole-cell current. A more complete characterization of these currents will be presented elsewhere.…”

“…In principle, the modulation of excitation by products of cell metabolism or by second messengers could be studied by monitoring the time course of the underlying ionic currents. Unfortunately, B cells rapidly lose their responsiveness to glucose during the first several minutes of conventional 'whole-cell' patch-clamp recording, and critical components of excitability, such as Ca" channels rapidly 'run-down' [2], a phenomenon commonly referred to as 'wash-out'.…”

Somatostatin release, electrical activity, membrane currents and exocytosis in human pancreatic delta cells

“…These bursts of action potentials are likely to underlie the intracellular Ca 2+ concentration [Ca 2+ ] i oscillations reported in delta cells [11,12,21,22], although the frequency of the [Ca 2+ ] i oscillations was slightly lower (<1/min) than that of the electrical bursts observed here (2-5/min). It has been proposed, based on both experimental and theoretical considerations, that oscillatory electrical activity in mouse beta cells depends on cell coupling [23,24]. However, the finding that high-frequency bursts of action potentials can be recorded from individual human delta cells suggests that cell coupling is not required for such electrical activity to occur.…”

Ligustrazine selectively blocks ATP‐sensitive K+ channels in mouse pancreatic β cells

“…Single pancreatic @ cells of NMRI mice were isolated and maintained in primary tissue culture for up to 3 days as previously described [2,4] and their K+ currents were recorded using the whole-cell configuration of the patch clamp technique 151. The extracellular medium contained (in mM); NaCl, 135; KCI, 5; MgS04, 1.2; CaCla, 2.5; NaOH-HEPES, 5; 21-24"C, pH 7.4.…”