Heat stress, via its effects on muscle intracellular Ca2+ concentrations ([Ca2+]i), has been invoked as a putative therapeutic countermeasure to Type 1 diabetes-induced muscle atrophy. Using in vivo muscle preparation we tested the hypothesis that impaired muscle Ca2+ homeostasis in type I diabetic rats is due to attenuated heat stress tolerance mediated via TRPV1. Male Wistar rats were assigned to 1 of 4 groups: 1.control 30oC (CONT 30oC), 2.CONT 40oC, 3.diabetes 30oC (DIA 30oC), 4.DIA 40oC. 40oC was selected because it just exceeds the TRPV1 activation threshold. Spinotrapezius muscles were exteriorized in vivo and loaded with the fluorescent Ca2+ probe Fura-2AM. [Ca2+]i was estimated over 20min using fluorescence microscopy in quiescent muscle held at the required temperature using calibrated heat source applied to the ventral muscle surface. Western blotting was performed to determine the protein expression levels of TRPV1 in spinotrapezius muscle. After 20min of heat stress, the CONT 40oC condition induced a 12.3% [Ca2+]i elevation that was absent from the DIA 40oC or other conditions. Thus, no significant differences were found among DIA 40oC, DIA 30oC and CONT 30oC. TRPV1 protein expression was decreased by 42.0% in DIA compared with CONT (P<0.05) and, unlike CONT, heat stress did not increase TRPV1 phosphorylation. In conclusion, diabetes suppresses TRPV1 protein expression and function and inhibits the elevated myocyte [Ca2+]i evoked normally by heat stress. These results suggest that capsaicin or other therapeutic strategies to increase Ca2+ accumulation via TRPV1 might be more effective than hyperthermic therapy for Type I diabetic patients.
Type I Diabetes Suppresses Intracellular Calcium Ion Influx by Heat Stress in Rat Skeletal Muscle
