SUMMARY1. Membrane currents through the Ca2+ channel were studied in a hybridoma cell line (MAb-7B) constructed by fusion ofSI94 myeloma cells and splenic B lymphocytes from the mouse. The whole-cell variation of the patch-electrode voltage-clamp technique was used. 3. Both inward and outward currents showed voltage-dependent inactivation with the same membrane potential dependence of steady-state inactivation.4. The decay time constant of the current decreased from about 27 ms at -44 mV to a saturation value of 16 ms at about -20 mV, and remained at this value even when the current became outward.5. From the above results both the inward and outward currents were considered to flow through Ca2+ channels. Y. FUKUSHIMA AND S. HAGIWARA 11. The suppression of the monovalent currents by Ca2+ and Mg2+ showed different voltage dependences. The suppression by Ca2+ increased and then decreased as the membrane potential was made negative, whereas the suppression by Mg2+ increased monotonically. This difference can be explained by considering the fact that Ca2+ is permeant and Mg2+ is impermeant through the Ca2+ channel.12. Under certain conditions the Ca2+ inward current coexisted with the monovalent inward current.13. The selectivity of the Ca2+ channel for monovalent cations in media containing low concentrations of divalent cations was evaluated from the reversal potential. Permeability ratios calculated were 1-0 for Na+, 0-8 for K+, 0-6 for Rb+ and 035 for Cs+. The ability of monovalent cations to carry the outward current at large positive potentials showed the same sequence.

1. The kinetics of the anomalous K current produced by blocking cations Na, Cs and Sr were analysed by single channel recording in the tunicate egg cell.2. The open-close kinetics in a single channel with the presence of blocking cation were consistent with the blocking kinetics of the total anomalous K current. The open-close kinetics in a single anomalous K rectifier channel could be regarded as the first order transition between the open and closed states.3. The closing rate constants of the single channel for the first order transition increased almost linearly on a semilogarithmic scale as the membrane potential became more negative, while the opening rate constants decreased and then increased, showing the minimum at a certain potential level. The latter indicated that the channel was released from the blocking by excessive hyperpolarization.4. The opening rate constant increased in spite of the fixed concentration of the blocking cation (10 muM-Cs), when the external K concentration was raised from 200 mM to 400 mM. This result suggested that there are interactions within the channel between the blocking cation and the K ion.5. When there were two kinds of blocking cations such as Na and Cs, the kinetic properties in a single channel indicated that the two kinds of blocking cations blocked the single channel independently.6. The single channel conductance of the anomalous K rectifier in 200 mM-Na-containing 200 mM-K solutions was about 1.5 times larger than that in Na-free 200 mM-K solutions.7. The single channel conductances in 100, 200 and 400 mM-K solution with 10 muM-Cs were 5.0, 7.1 and 12.3 pS respectively, being roughly proportional to the square root of the K concentration.8. The density of the anomalous K rectifier channel in the tunicate egg cell was 0.039/mum(2).9. The amplitude of the single channel current increased with the rise of temperature, the Q(10) being 1.5.

SUMMARY1. The electrical properties of the cell membrane of clonal cytotoxic T lymphocytes in the mouse were studied by using the whole cell variation of the patch electrode voltage-clamp technique.2. Outward currents were activated with an exponential time course of several milliseconds time constant when the membrane potential was made more positive than -50 to -40 mV. This current is not activated as a result of Ca2+ entry.3. The estimated reversal potential of the current indicates that the current is predominantly carried by K+. The activation kinetics depend only on membrane potential, not on [K+]O.4. The amplitude of the current decreases exponentially with time constants of several hundred milliseconds during a maintained voltage pulse, due mainly to a decrease in conductance.5. Recovery from inactivation roughly followed a single exponential time course with a time constant of tens of seconds; this time constant depended upon not only the membrane potential but also the amount of initial inactivation.6. The current is suppressed by quinidine and tetraethylammonium, their halfsuppression concentrations being 23 /LM and 14 mm respectively.

Aims/IntroductionThe objective of the present study was to clarify the validity of β‐cell function‐related parameters for predicting the insulin requirement of Japanese type 2 diabetic patients.Materials and MethodsIn 188 patients with type 2 diabetes who had been admitted to the University of Toyama Hospital (Toyama, Japan) without receiving insulin therapy, we carried out a cross‐sectional study examining the relationship between the homeostasis model assessment of β‐cell function (HOMA‐β) and C‐peptide‐based indices, and also carried out a retrospective study to examine the utility for predicting insulin requirement of several β ‐cell function‐related indices using a receiver operating characteristic (ROC) curve analysis.ResultsThe secretory units of islets in transplantation index (SUIT) had the strongest correlation with HOMA‐β, followed by the fasting serum C‐peptide immunoreactivity index (CPI); the fasting serum C‐peptide immunoreactivity itself (F‐CPR) had the least correlation. The CPI, HOMA‐β and SUIT were significantly lower in the insulin‐requiring group than in the non‐insulin‐requiring group, even after adjustments for confounding factors (P < 0.01). The areas under the ROC curve for insulin requirement were 0.622, 0.774, 0.808, and 0.759 for F‐CPR, CPI, SUIT, and HOMA‐β, respectively. The cut‐off values of SUIT, CPI, and HOMA‐β for an over 80% specificity for the prediction of insulin therapy were 23.5, 1.00, and 14.9, respectively.ConclusionsThe present study shows that SUIT is the best predictor of insulin requirement among these β‐cell function‐related markers.