The effects of heavy long-term exercise on ventricular myocyte shortening and intracellular Ca2+ in streptozotocin-induced diabetic rat.
OBJECTIVE
This study investigated whether exercise training, initiated at the onset of diabetes, could preserve the contractile properties of ventricular myocytes.


METHODS
The effects of a heavy exercise training program on shortening and intracellular Ca(2+) in unloaded ventricular myocytes from streptozotocin (STZ)-induced diabetic rats were examined. Animals were divided into four groups: control sedentary (CS), diabetic sedentary (DS), control heavy exercise (CHE), and diabetic heavy exercise (DHE). Exercise protocol: 5x60 min/week, 18 m/min, 5% gradient. Exercise training began 1 week after STZ treatment and continued for 12-23 (mean 17.5) weeks.


RESULTS
Diabetes induced prolongation of time-to-peak (TPK) shortening (124+/-2 ms in DS compared to 97+/-2 ms in CS rats), which was further increased by exercise (133+/-3 ms in DHE and 112+/-2 ms in CHE myocytes). Diabetes had no significant effects on time-to-half (THALF) relaxation of shortening (61+/-2 ms in DS compared to 56+/-2 ms in CS myocytes). Exercise induced significant prolongation of THALF in control (66+/-3 ms) but not in diabetic (69+/-3 ms) myocytes. Diabetes, though not exercise, significantly prolonged TPK (76+/-3 ms in DS compared to 64+/-2 ms in CS) and THALF recovery (160+/-5 ms in DS compared to 118+/-4 ms in CS) of the Ca(2+) transient. Neither diabetes nor exercise had significant effects on the amplitude of myocyte shortening and the Ca(2+) transient.


CONCLUSIONS
Heavy long-term exercise alters the dynamics but not the amplitude of unloaded myocyte contraction in the STZ-induced diabetic rat.
Howarth
Frank Christopher
FC
Department of Physiology, Faculty of Medicine and Health Sciences, United Arab Emirates University, P.O. Box 17666, Al Ain, UAE. chris.howarth@uaeu.ac.ae
Almugaddum
Fadwa A
FA
Qureshi
Muhammud A
MA
Ljubisavljevic
Milos
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D048429:Cell Size; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology* / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000009:adverse effects* / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013311:Streptozocin; D013997:Time Factors
D013311:Streptozocin; D002118:Calcium