Cardiac contractile dysfunction is frequently reported in human patients and experimental animals with type-1 diabetes mellitus. The aim of this study was to investigate the voltage-dependence of contraction in ventricular myocytes from the streptozotocin (STZ)-induced diabetic rat. STZ-induced diabetes was characterised by hyperglycaemia and hypoinsulinaemia. Other characteristics included reduced body and heart weight and raised blood osmolarity. Isolated ventricular myocytes were patched in whole cell, voltage-clamp mode after correcting for membrane capacitance and series resistance. From a holding membrane potential of -40 mV, test pulses were applied at potentials between -30 and +50 mV in 10 mV increments. L-type Ca2+ current (I Ca,L) density and contraction were measured simultaneously using a video-edge detection system. Membrane capacitance was not significantly altered between control and STZ-induced diabetic myocytes. The I Ca,L density was significantly (p < 0.05) reduced throughout voltage ranges (-10 mV to +10 mV) in myocytes from STZ-treated rats compared to age-matched controls. Moreover, the amplitude of contraction was significantly reduced (p < 0.05) in myocytes from STZ-treated rats at all test potentials between -20 mV and +30 mV. However, in electrically field-stimulated (1 Hz) myocytes, the amplitude of contraction was not altered by STZ-treatment. It is suggested that in field-stimulated myocytes taken from STZ-induced diabetic hearts, prolonged action potential duration may promote increased Ca2+ influx via the sodium-calcium exchanger (NCX), which may compensate for a reduction in Ca2+ trigger through L-type-Ca2+-channels and lead to normalised contraction.

No abstract

Trauma and injury necessitate the use of various surgical interventions, yet such procedures themselves are invasive and often interrupt synaptic communications in the nervous system. Because anesthesia is required during surgery, it is important to determine whether long-term exposure of injured nervous tissue to anesthetics is detrimental to regeneration of neuronal processes and synaptic connections. In this study, using identified molluscan neurons, we provide direct evidence that the anesthetic propofol blocks cholinergic synaptic transmission between soma-soma paired Lymnaea neurons in a dose-dependent and reversible manner. These effects do not involve presynaptic secretory machinery, but rather postsynaptic acetylcholine receptors were affected by the anesthetic. Moreover, we discovered that long-term (18-24 h) anesthetic treatment of soma-soma paired neurons blocked synaptogenesis between these cells. However, after several hours of anesthetic washout, synapses developed between the neurons in a manner similar to that seen in vivo. Long-term anesthetic treatment of the identified neurons visceral dorsal 4 (VD4) and left pedal dorsal 1 (LPeD1) and the electrically coupled Pedal A cluster neurons (PeA) did not affect nerve regeneration in cell culture as the neurons continued to exhibit extensive neurite outgrowth. However, these sprouted neurons failed to develop chemical (VD4 and LPeD1) and electrical (PeA) synapses as observed in their control counterparts. After drug washout, appropriate synapses did reform between the cells, although this synaptogenesis required several days. Taken together, this study provides the first direct evidence that the clinically used anesthetic propofol does not affect nerve regeneration. However, the formation of both chemical and electrical synapses is severely compromised in the presence of this drug. This study emphasizes the importance of short-term anesthetic treatment, which may be critical for the restoration of synaptic connections between injured neurons.

We have investigated and compared GH and epidermal growth factor (EGF) signaling in primary human skin fibroblasts from normal subjects and subjects with GH-binding protein-positive Laron syndrome (LS). In normal human fibroblasts, GH and EGF activate the tyrosine phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT5b; in LS fibroblasts, EGF does, but GH does not. GH also activates the tyrosine phosphorylation of Janus kinase (JAK)2 in normal, but not LS, fibroblasts. Similarly, both GH and EGF activate MAPK in normal fibroblasts, but only EGF does in the LS fibroblasts. As in the 3T3-F442A mouse preadipocyte cell line, GH signaling to mitogen-activated protein kinase is partially inhibited by wortmannin treatment, indicating a role for phosphatidylinositol 3-kinase (PI3K) in this signaling pathway. The exogenous expression of the GH receptor in one family of LS fibroblasts (H1) but not the other (M) restores signaling to a STAT5 reporter element. Together, these results indicate that the mechanism of defective GH signaling in two families of LS fibroblasts are different but that both occur at a level close to, and specific for, the GH receptor.

General anaesthetics have previously been shown to have profound effects on myocardial function. Moreover, many patients suffering from diabetes mellitus are anaesthetised during surgery. This study investigated compromised functioning of cardiac myocytes from streptozotocin (STZ)-induced diabetic rats and the additive effects of halothane on these dysfunctions. Ventricular myocytes were isolated from 8 to 12 weeks STZ-treated rats. Contraction and intracellular free calcium concentration ([Ca2+]i) were measured in electrically field-stimulated (1 Hz) fura-2-AM-loaded cells using a video-edge detection system and a fluorescence photometry system, respectively. L-type Ca2+ current was measured in whole cell, voltage-clamp mode. Halothane significantly (p < 0.01) depressed the amplitude and the time course of the Ca2+ transients in a similar manner in myocytes from control and STZ-treated rats. However, the effect of halothane on the amplitude of shortening and L-type Ca2+ current was more pronounced in myocytes from STZ-treated animals compared to age-matched controls. Myofilament sensitivity to Ca2+ was significantly (p < 0.01) increased in myocytes from STZ-treated rats compared to control. However, in the presence of halothane the myofilament sensitivity to Ca2+ was significantly (p < 0.05) reduced to a greater extent in myocytes from STZ-treated rats compared to controls. In conclusion, these results show that contractility, Ca2+ transport and myofilament sensitivity were all altered in myocytes from STZ-treated rats and these processes were further altered in the presence of halothane suggesting that hearts from STZ-induced diabetic rats are sensitive to halothane.