Insulin stimulates the L-type Ca2+ current in rat cardiac myocytes.

OBJECTIVE: The aim was to study the L-type calcium current (ICa,L) in cardiac myocytes as a possible target of insulin in the regulation of cardiac function. METHOD: Using the whole-cell configuration of the patch-clamp technique, we investigated the stimulation of ICa,L by insulin in isolated rat ventricular myocytes. RESULTS: The stimulation of ICa,L by insulin was dose-dependent (EC50 = 33 nM) and reversible. Maximum stimulation of ICa,L over basal ICa,L was 86 +/- 11% (n = 25) at 1 microM insulin. Insulin (1 microM) shifted the current-voltage relationship and potential-dependent availability of ICa,L to more negative potentials by about 3.5 and 1.5 mV, respectively. The maximum conductance of ICa,L was increased by 1 microM insulin, from 26 +/- 4 to 39 +/- 5 nS (n = 11). Isoproterenol (100 nM), which stimulated ICa,L by 156 +/- 23% (n = 10) over basal ICa,L, acted faster than insulin. The half-maximum stimulation of ICa,L by isoproterenol and insulin was reached after 44 +/- 5 and 80 +/- 9 s, respectively. Insulin and isoproterenol responses were not additive. Insulin (1 microM) and isoproterenol (100 nM) stimulation of ICa,L was inhibited by Rp-cAMPS (1 mM) to 12 +/- 3 and 32 +/- 4%, respectively. Insulin (1 microM) increased cAMP content in rat cardiomyocytes by about two-fold. Insulin-like growth factor-1 (IGF-1; 5 microM) increased ICa,L by only 5.9 +/- 0.9% (n = 6). CONCLUSIONS: Our data show that insulin stimulates the L-type calcium current in isolated rat ventricular myocytes in a dose-dependent and reversible manner and suggest that this effect is mediated by insulin receptors and the cAMP-dependent protein kinase.

Stimulation of L-type Ca2+ current in human atrial myocytes by insulin.

OBJECTIVE: The L-type calcium current (ICa,L) in isolated human atrial myocytes was investigated as a possible target of insulin in the regulation of cardiac function. METHODS: Atrial myocytes were obtained from patients undergoing cardiac surgery. Using the whole-cell configuration of the patch-clamp technique, we investigated the stimulation of ICa,L by insulin in single human atrial myocytes. RESULTS: We found a dose-dependent stimulation of ICa,L by insulin at concentrations of 100 nM, 1 microM and 10 microM. Maximum stimulation of ICa,L over basal ICa,L was 140 +/- 12% (n = 11) at 10 microM insulin. The maximum conductance of ICa,L was increased by 10 microM insulin from 4.0 +/- 0.3 nS to 8.3 +/- 1.0 nS (n = 6). The stimulation of ICa,L by insulin was dose-dependent and reversible. Isoproterenol (10 nM) that stimulates ICa,L by 271 +/- 48% (n = 10) over basal ICa,L acted faster than insulin. The half-maximum stimulation of ICa,L by isoproterenol and insulin (10 microM) was reached after 31 +/- 2 s and 52 +/- 5 s, respectively. The insulin effect shown was totally reversed by acetylcholine (3 microM) which is known to inhibit adenylyl cyclase activity/cAMP-production via Gi-proteins. Also, the selective insulin receptor tyrosine kinase inhibitor (hydroxy-2-naphthanelyl-methyl)phosphonic acid completely inhibited the insulin induced effect. CONCLUSION: Our data show that insulin stimulates the L-type calcium current in isolated human atrial myocytes in a dose-dependent and reversible manner which appears to involve the insulin receptor tyrosine kinase. Insulin regulation of ICa,L in human atrial myocytes may be an interesting system for the analysis of the metabolic syndrome in man.

[Monitoring of 131I incorporation in nuclear medicine personnel by self accomplished measurements]. / 131I-Inkorporationsüberwachung in der Nuklearmedizin durch regelmässige Eigenmessung des Personals.

AIM: The personnel in nuclear medicine therapy wards must be monitored according to German guidelines for incorporations of (131)I. A surveillance with the employees measuring themselves similarly to the autonomous contamination survey using hand-foot-clothing monitors is presented as an alternative to the monitoring according to the official guidelines. METHOD: The employees use a dedicated device to measure themselves every working day. The automatic individual positioning of the device ensures reliable and reproducible results. The thyroid dose is determined from the measured time activity curve. The individual values of depth and mass of the thyroid are taken into account for activity measurement and dose evaluation, respectively. RESULTS: The employees measure themselves regularly and utilize the device to check for activities in the thyroid at an early stage after suspected incorporation. The almost complete surveillance permits a dosimetry with slight uncertainty. The determined thyroid doses of all monitored persons average to 0.35 mSv per month. CONCLUSION: The incorporation surveillance by autonomous monitoring allows a more reliable and more precise dosimetry than the monitoring according to the official guidelines. Despite numerous measurements the practice saves time and money as a result of the automation.