Objective: To investigate the effects and mechanism of verapamil preventing ischemia/reperfusion (I/R) injury by cardiac performance intracellular free [Ca(2+)](i) and L-type calcium current (I(Ca-L)) in cardiomyocytes of diabetes mellitus rats.
Methods: Diabetic rats were streptozotocin-induced and received verapamil (8 mg×kg(-1)×d(-1)) from 6 - 14 weeks old. The in vitro heart models of I/R rats were randomly divided into normal control group diabetes group, verapamil control group. the changes of heart functions were observed through a Langendorff-perfusion system. The fluorescence intensity of intracellular Ca(2+) was detected with Fluo-3/AM loading by laser scanning confocal microscope. I(Ca-L) was recorded by the whole-cell technique of patch clamp in enzymatically dissociated single rat ventricular myocytes.
Results: (1) In verapamil diabetes group, the values of left ventricular developed pressure [(91.3 ± 4.6) mm Hg], diastolic end pressure [(1535 ± 280) mm Hg], the maximum rising rates of left ventricular pressure [(5833 ± 256) mm Hg/s] and coronary arterial flow [(13.7 ± 0.9) ml/min] were all significantly increased, and the maximum dropping rates of left ventricular pressure [(3504 ± 319) mm Hg/s] was obviously decreased (compared with diabetes group, P < 0.01, respectively). (2) The fluorescence intensities of intracellular free Ca(2+)[(155.6 ± 10.9) nmol/L] in verapamil diabetes group were significantly reduced compared with diabetes group (245.2 ± 17.5 nmol/L, P < 0.01). (3) When clamp voltage was -20mV, I(Ca-L) was (-6.81 ± 0.76) pA/pF in verapamil diabetes group (compared with normal group (-8.17 ± 2.07) pA/pF, P < 0.05, and with diabetes group (-3.21 ± 0.54) pA/pF, P < 0.01, and with verapamil control group (-7.14 ± 2.17) pA/pF, P > 0.05). The current-voltage curve was changed to the lower position with -20mV of peak clamp potential in verapamil diabetes group compared with diabetes group.
Conclusion: A poor heart function is closely correlated with a rising [Ca(2+)]i and a declining I(Ca-L) associated with I/R injury in diabetic rats hearts. Along-term verapamil therapy may significantly improve the severe cardiac impairment. The mechanism is probably attributed to the fact that verapamil can adjust I(Ca-L) influx, normalize the balance of intercellular [Ca(2+)]i, and block the Ca(2+) overload trigger by the effects of Ca(2+)-induced Ca(2+) release in diabetic cardiomyocytes.