Intracellular and extracellular angiotensin II enhance the L-type calcium current in the failing heart.
The influence of intracellular and extracellular angiotensin II (Ang II) on the L-type calcium current of cardiomyocytes isolated from cardiomyopathic hamsters was investigated. The results indicated that Ang II (10(-8) mmol/L), added to the bath, increased the peak inward calcium current (I(Ca)) density by 37+/-3.4% (P<0.05), an effect that depends on the activation of protein kinase C. Intracellular administration of the same dose of Ang II (10(-8) mmol/L) also elicited an increase of peak I(Ca) density but enhanced the rate of I(Ca) inactivation, an effect not seen with extracellular Ang II. Moreover, in control animals, no change in the rate of I(Ca) inactivation was seen with intracellular Ang II. Thapsigargin (1 micromol/L), a potent inhibitor of sarcoplasmic reticulum (SR) ATPase, which depletes the SR, decreased the rate of I(Ca) inactivation elicited by intracellular Ang II, although the cytoplasmic calcium concentration was highly buffered with 10 mmol/L EGTA. These findings might indicate that intracellular Ang II releases calcium from the SR and inactivates I(Ca). The effect of intracellular Ang II on peak I(Ca) was not altered by extracellular losartan (10(-7) mmol/L), supporting the notion that the peptide acted intracellularly. Other studies showed that intracellular Ang I administration (10(-8) mmol/L) enhanced the peak I(Ca) density and the rate of I(Ca) inactivation, an effect that was reduced by intracellular enalaprilat (10(-8) mmol/L). Moreover, intracellular enalaprilat by itself reduced the peak I(Ca) density. These observations might indicate that endogenous Ang II is contributing to I(Ca) modulation in the failing heart.
De Mello
Walmor C
WC
Department of Pharmacology, University of Puerto Rico, San Juan, PR 00936-5067. wmello@rcm.upr.edu
Monterrubio
Jose
J
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000803:Angiotensin I / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology*; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000809:Angiotensins / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D009202:Cardiomyopathies / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured / Q000187:drug effects; D006224:Cricetinae; D015773:Enalaprilat / Q000494:pharmacology; D004789:Enzyme Activation; D045604:Extracellular Fluid; D007424:Intracellular Fluid; D019808:Losartan / Q000494:pharmacology; D008297:Male; D008647:Mesocricetus; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D019311:Staurosporine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D047228:Angiotensin II Type 1 Receptor Blockers; D000806:Angiotensin-Converting Enzyme Inhibitors; D000809:Angiotensins; D020746:Calcium Channels, L-Type; C498038:angiotensin II, Val(5)-Ala(8)-; D000804:Angiotensin II; D019284:Thapsigargin; D000803:Angiotensin I; D011493:Protein Kinase C; D000251:Adenosine Triphosphatases; D015773:Enalaprilat; D019311:Staurosporine; D019808:Losartan