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M Kakei

Publications and source records attributed to M Kakei.

16 recordsLinked to original sources
PubMed1992

Single pancreatic beta-cells from normal rats exhibit an initial decrease and subsequent increase in cytosolic free Ca2+ in response to glucose.

Since it was reported that glucose stimulation initially lowers as well as subsequently raises the cytosolic free calcium concentration [( Ca2+]i) in pancreatic islet cells from hyperglycemic ob/ob mice, it has been argued whether the lowering of [Ca2+]i is physiological or artifactual. In the present study, [Ca2+]i in single pancreatic beta-cells from normal rats was measured by Fura-2 microfluorometry. Following elevation of the glucose concentration from 2.8 mM (basal) to 16.7 mM, a bimodal change in [Ca2+]i, an initial decrease and subsequent increase, was demonstrated. When the basal glucose concentration was raised to 5.6 mM, the stimulation with 16.7 mM glucose also induced the decrease in [Ca2+]i in the majority of the cells, though the amplitude of the decrease was reduced. An elevation of the glucose concentration from 2.8 to 5.6 mM induced the decrease in [Ca2+]i but not usually the increase in [Ca2+]i. Removal of extracellular Ca2+ eliminated the increase in [Ca2+]i without affecting the decrease in [Ca2+]i. Thus, the decrease and increase in [Ca2+]i were clearly dissociated under certain conditions. In contrast, mannoheptulose (an inhibitor of glucose metabolism) inhibited both the decrease and increase in [Ca2+]i. These results demonstrate that the glucose-induced bimodal change in [Ca2+]i is a physiological response of islet beta-cells, and that the decrease and increase in [Ca2+]i are generated by mutually-independent mechanisms which are operated through glucose metabolism by islet beta-cells.

Animals↗
PubMed1990

[The effect of repeated small doses of radiation on cell killing and repair capacity in plateau phase C3H 10T 1/2 cells].

Using plateau phase C3H 10 T 1/2 cells, we studied the effect of multiple-dose irradiation on the repair capacity of cells after further irradiation. Cells were irradiated with repeated doses of 2.5 Gy delivered two fractions per day at 6 to 7 hours interval. The cell survival after exposure to 1 to 9 fractions was lower above fractions as compared to that predicted by calculating from single dose survival curve by assuming that cells retain their capacity to repair radiation damage after each fraction. Repair kinetics experiments showed that cells were less able to repair only slow type potentially lethal damage after test dose following multiple dose irradiations. Thus, it would appear that an enhancement of the lethal expression of potentially lethal damage of three types of damage may, at least in part, contribute to the difference between the cell survival curve after multiple fractions and that predicted by calculation.

Animals↗
PubMed1989

[Renal accumulation of technetium-99m-labeled bone imaging agents in patients treated with cisplatin].

As the routine follow-up studies in patients with malignant diseases, bone scintigraphy is often performed to detect bone metastasis, before, during and/or after the treatments. Among these patients who were treated, especially, with CDDP, we often encountered the markedly increased renal radioactivity during the follow-up period by bone scintigraphy. In this study, 68 patients with 76 bone scintigraphy performed within 30 days after the administration of CDDP were evaluated. Forty-five of the 76 bone scintigraphy (60.5%) in the 68 patients exhibited more prominent accumulation of the radionuclide in the kidneys than that normally seen. Among them, twenty-four cases (31.6%) showed markedly increased accumulation of the radionuclide in the kidneys so called the "hot kidneys", when the bone scintigraphy was performed later than 3 weeks after the treatment with CDDP. Moreover, the frequency of the "hot kidneys" were well correlated with the degree of renal damage in terms of serum creatinine levels. These findings suggest that the "hot kidneys" might represent the presence of transient renal damage caused by the administration of CDDP. As the causes of this finding called as the "hot kidneys", various factors and/or many causes are reported recently, however, the highest incidence of this phenomenon is thought to be occurred by CDDP as the factor of drug incidence.

Adult↗
PubMed1989

The ATP- and tolbutamide-sensitivity of the ATP-sensitive K-channel from human pancreatic B cells.

The ATP- and sulphonylurea-sensitivity of the ATP-sensitive K-channel was measured in human pancreatic B cells. In inside-out patches, half-maximal inhibition of channel activity was produced by 10 mumol/l ATP (with 2 mM Mg2+) and ATP-inhibition was partially antagonised by ADP. A significantly lower sensitivity to ATP was found in whole-cell recordings. Tolbutamide inhibited whole-cell ATP-sensitive K-currents half-maximally at 18 mumol/l; the sensitivity to tolbutamide was somewhat less in the inside-out patch. Ca-activated K-channels were unaffected by tolbutamide (10 mmol/l). These results resemble those found for rodent B cells and suggest that sulphonylureas exert their therapeutic effects in Type 2 (non-insulin dependent) diabetes by inhibition of the ATP-sensitive K-channel.

Adenosine Triphosphate↗
PubMed1989

Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells.

1. The patch-clamp method has been used to study the selectivity of single ATP-sensitive potassium channels in excised membrane patches from dissociated rat pancreatic beta-cells. 2. In symmetrical K+ concentrations the current-voltage relation of this channel showed slight inward rectification. The K+ permeability coefficient was 1.05 x 10(-13) cm3/s ([K+]o = 140 mM; 20 degrees C) in the inside-out patch and somewhat smaller when measured under the same conditions in the outside-out configuration (0.86 x 10(-13) cm3/s). 3. When intracellular Rb+ replaced K+, inward K+ currents were unaffected but the outward currents carried by Rb+ were substantially smaller. The extent of the reduction in the outward currents depended on the internal Rb+/K+ ratio and increased as [Rb+]i was raised. Both inward and outward Rb+ currents were blocked by 1 mM-ATP. No currents were measurable in symmetrical 140 mM-Rb+ solutions. 4. With 140 mM [K+]o and 140 mM [Rb+]i the single-channel current-voltage relation reversed at +8 mV and the potential at which the variance of the ATP-sensitive current was least was shifted by 6 mV to more positive potentials. These data suggest a PRb/PK ratio of around 0.7. 5. Outward Rb+ currents were reduced at all potentials in inside-out patches exposed to 107 mM-Rb+ solution intracellularly and 5 mM-K+ externally. 6. Partial replacement of external K+ with Rb+ substantially reduced the inward currents recorded from outside-out patches and also decreased outward K+ currents. 7. In outside-out patches, the addition of 1 mM-Rb+ to the external solution produced a block of inward K+ currents that initially increased and then decreased again with hyperpolarization. This suggests that the Rb+ block of K+ currents is voltage dependent and that Rb+ acts as a permeant blocker of K+ currents. 8. The sodium permeability of the channel, relative to that of potassium, was 0.39 for internal Na+ and 0.007 for external Na+ ions. 9. We conclude that Rb+ serves as an acceptable tracer for K+ in efflux studies when changes in K+ flux through ATP-sensitive K+ channels are of interest but that the magnitude of such fluxes will be considerably underestimated.

Adenosine Triphosphate↗
PubMed1989

ATP-sensitive K+ channels in rat pancreatic beta-cells: modulation by ATP and Mg2+ ions.

1. The inside-out configuration of the patch-clamp method was used to study the effects of MgATP, free ATP and Mg2+ on single ATP-sensitive K+ channel currents in rat pancreatic beta-cells. 2. Magnesium ions caused a marked reduction of channel activity: 5 mM-free Mg2+ produced a 50% reduction in the activity of inward currents recorded at -60 mV in symmetrical K+ concentrations. 3. Inhibition of channel activity by MgATP does not involve phosphorylation as both free ATP (i.e. ATP in the absence of divalent cations) and non-hydrolysable ATP analogues were effective inhibitors. 4. Magnesium ions produced a striking reduction in the ability of ATP (total) to inhibit channel activity. When channel activity was plotted as a function of the total ATP concentration, the Ki for channel inhibition was 4 microM in Mg2(+)-free solution, compared to a Ki of 26 microM in the presence of 2 mM-Mg2+. The shape of the relationship between channel activity and the total ATP concentration was not changed by Mg2+. When channel activity was plotted as a function of the free ATP concentration, however, Mg2+ had little effect on Ki. This suggests that free ATP is the more potent inhibitor of channel activity and that MgATP has little inhibitory effect. 5. ATP analogues that dissociate only as far as the tribasic form were also able to inhibit channel activity. This suggests that both ATP4- and ATPH3- can block the channel. 6. Like ATP, ADP was more effective at inhibiting channel activity in the absence of Mg2+, that is as the free base. The non-hydrolysable ATP analogues AMP-PNP and AMP-PCP, however, were more effective in the presence of Mg2+. 7. It is suggested that (1) the potency of inhibition is related to the amount of negative charge carried by the ion and (2) the intracellular concentration of free ATP will be an important modulator of channel activity in the intact beta-cell.

Adenosine Diphosphate↗
PubMed1987

ATP-sensitive K+ channels in human isolated pancreatic B-cells.

Glucose-stimulated insulin release from rodent pancreatic B-cells is thought to be initiated by the closing of ATP-sensitive K+ channels in the plasma membrane as a consequence of glucose metabolism. We have identified an ATP-sensitive K+ channel in membrane patches excised from human B-cells which is similar to that found in rodent B-cells in conductance, kinetics, ATP sensitivity and its inhibition by sulphonylureas. In man, the ATP-sensitive K+ channel may also have a central role in glucose-stimulated insulin secretion and may be (linked to) the receptor for the hypoglycemic sulphonylureas.

Adenosine Triphosphate↗
PubMed1987

A microflow superfusion system for use with excised membrane patches.

A new method for rapidly changing the solution superfusing excised membrane patches is described. The main advantage of this method over previous rapid exchange methods is that it is possible to use very small quantities of solution (minimal volume about 100 microliters). The method consists of inserting the pipette tip, after obtaining an excised patch, into a small tube which can be independently perfused. Air bubbles are used to separate different solutions and to produce rapid "step" changes of solution. To test this method we examined the rate of change of: the pipette resistance produced in response to changing to a solution of lower conductivity, the amplitude of single K-channel currents in response to changing external K. The results suggest that the solution exchange is essentially a step function and is complete within 10-20 ms. The recording is briefly interrupted during the time taken for the passage of the air bubble past the pipette tip (less than 250 ms). In general, the passage of the air bubble did not affect the seal resistance. This method will be particularly useful for studies of the interactions of single ionic channels with chemicals which can only be obtained in small quantities.

Animals↗
PubMed1986

The potassium current activated by 2-nicotinamidoethyl nitrate (nicorandil) in single ventricular cells of guinea pigs.

Membrane currents through potassium channels activated by nicorandil, which has a potent coronary vasodilating action, have been studied in ventricular cells of guinea pigs by using the single pipette whole-cell clamp technique. In the presence of 0.1 mM nicorandil, the duration of the action potential was shortened from 196 to 145 ms. Nicorandil markedly increased outward currents at potentials positive to the resting potential. When the difference in the currents before and after the application of nicorandil were plotted against the membrane potential, the current-voltage relation reversed close to the potassium equilibrium potential. The difference current during depolarizing pulses showed no time-dependent relaxation. These results indicate that the current evoked by nicorandil is carried by K+ ions and has voltage-independent kinetics. Power-density spectra obtained in the presence of nicorandil were fitted well by a single Lorentzian curve with a corner frequency of 4.4 Hz. The amplitude of the single-channel unit current was estimated from the relation between the variance and the mean current, and was 0.27 +/- 0.1 pA (n = 7) at -35 mV. The estimated slope conductance was 4.6 +/- 1.7 pS. Nicorandil did not affect Ca2+ currents. It is concluded that nicorandil activates a small-conductance K+ channel without affecting the Ca2+ channel.

Action Potentials↗
PubMed1986

The ATP-sensitivity of K+ channels in rat pancreatic B-cells is modulated by ADP.

ATP-sensitive K+ channels in inside-out membrane patches from dispersed rat pancreatic B-cells were studied using patch-clamp methods. The dose-response curve for ATP-induced channel inhibition was shifted to higher concentrations in the presence of ADP (2 mM). In glucose-free solution, the total intracellular concentration of ATP was 3.8 mM and of ADP 1.5 mM; glucose (20 mM) increased ATP and decreased ADP by approx. 40%. These results suggest that both ADP and ATP may be involved in regulating the activity of the glucose-sensitive K+ channel in intact B-cells.

Adenosine Diphosphate↗
PubMed1985

Properties of adenosine-triphosphate-regulated potassium channels in guinea-pig ventricular cells.

A class of K channels in cardiac muscle is reversibly blocked by intracellular adenosine 5'-triphosphate (ATP). The characteristics of this K channel were studied by recording single-channel currents in ventricular cells isolated enzymatically from guinea-pig heart. The reversal potential of single-channel currents agreed well with the K equilibrium potential. Blockers of other K channels, such as tetraethylammonium and 4-aminopyridine, decreased the mean open time of the channel. The chord conductance increased as the 0.24th power of the K concentration on the outer surface of the membrane, and showed a marked inward-going rectification on strong depolarizations. The degree of rectification was larger with increasing Na concentration on the inner side of the membrane. The kinetics of the channel were almost voltage independent, but depended on the concentration of intracellular ATP. The conductance of the channel was not affected by ATP. When channel kinetics were examined in the presence of ATP, the distribution of open times and closed times was fitted well with a sum of two exponential components. When ATP concentration was increased, the time constants obtained from the open-time histogram decreased and those from the closed-time histogram increased, resulting in a decrease of the open-state probability. The channel was blocked by ATP, adenosine 5'-diphosphate,5'-adenylylimidodiphosphate, guanosine 5'-triphosphate and uridine 5'-triphosphate, but not by adenosine 5'-monophosphate, creatine phosphate, creatine or adenosine. Plots of the open-state probability versus the ATP concentration revealed Michaelis-Menten saturation kinetics with strong co-operativity of multiple receptor sites (Hill coefficient 3-4, concentration of half-saturation 0.5 mM). It was concluded that this K channel has three or four receptor sites selective for triphosphate nucleotide on the inner surface of the membrane, and that the channel is blocked through the binding of agonists to the receptors.

4-Aminopyridine↗