J Ren1. 1. Department of Pharmacology, Physiology, and Therapeutics, University of North Dakota School of Medicine, 501 N. Columbia Road, Grand Forks, ND 58203, USA. jren@medicine.nodak.edu
Abstract
OBJECTIVE: Insulin-like growth factor I (IGF-1) stimulates cardiac growth and contraction, but resistance to its action has been reported in diabetes. This study was to determine if IGF-1-induced cardiac contractile action is altered in rats genetically predisposed to diabetes. METHOD: Ventricular myocytes were isolated from spontaneously biobreeding diabetes-prone (BB/DP) rats and their diabetes-resistant littermates (BB/DR). Mechanical properties were evaluated in cardiomyocytes using a video-based edge-detection system. Myocytes were electrically stimulated at 0.5 Hz. Contractile properties analyzed included peak shortening (PS), time-to-PS (TPS) and time-to-90% relengthening (TR(90)). Intracellular Ca(2+) transients were measured as changes in fura-2 fluorescence intensity (DeltaFFI). RESULTS: Myocytes from BB/DP rats displayed increased PS, prolonged TPS and TR(90,) as well as reduced resting FFI compared to the BB/DR group. IGF-1 (10(-10)-10(-6) M) caused a dose-dependent increase in PS in myocytes from BB/DR but not BB/DP rats. The increase of PS was blunted by IGF-1 antagonist H-1356, phosphatidylinositol-3 (PI-3) kinase inhibitor wortmannin, but not tyrosine kinase inhibitor genistein. None of these agents affected responses to IGF-1 in BB/DP myocytes. Interestingly, IGF-1 elicited a comparable dose-dependent increase in Ca(2+) transients in myocytes from both BB/DR and BB/DP rats. CONCLUSION: These results suggest that the attenuation of IGF-1-induced cardiac contractile response in chemically-induced diabetes also exists in diabetes of genetic origin, possibly due to mechanisms involving PI-3 kinase and intracellular Ca(2+) sensitivity.
OBJECTIVE:Insulin-like growth factor I (IGF-1) stimulates cardiac growth and contraction, but resistance to its action has been reported in diabetes. This study was to determine if IGF-1-induced cardiac contractile action is altered in rats genetically predisposed to diabetes. METHOD: Ventricular myocytes were isolated from spontaneously biobreeding diabetes-prone (BB/DP) rats and their diabetes-resistant littermates (BB/DR). Mechanical properties were evaluated in cardiomyocytes using a video-based edge-detection system. Myocytes were electrically stimulated at 0.5 Hz. Contractile properties analyzed included peak shortening (PS), time-to-PS (TPS) and time-to-90% relengthening (TR(90)). Intracellular Ca(2+) transients were measured as changes in fura-2 fluorescence intensity (DeltaFFI). RESULTS: Myocytes from BB/DPrats displayed increased PS, prolonged TPS and TR(90,) as well as reduced resting FFI compared to the BB/DR group. IGF-1 (10(-10)-10(-6) M) caused a dose-dependent increase in PS in myocytes from BB/DR but not BB/DPrats. The increase of PS was blunted by IGF-1 antagonist H-1356, phosphatidylinositol-3 (PI-3) kinase inhibitor wortmannin, but not tyrosine kinase inhibitor genistein. None of these agents affected responses to IGF-1 in BB/DP myocytes. Interestingly, IGF-1 elicited a comparable dose-dependent increase in Ca(2+) transients in myocytes from both BB/DR and BB/DPrats. CONCLUSION: These results suggest that the attenuation of IGF-1-induced cardiac contractile response in chemically-induced diabetes also exists in diabetes of genetic origin, possibly due to mechanisms involving PI-3 kinase and intracellular Ca(2+) sensitivity.