Author:
Reading S A,Murrant C L,Barclay J K
Abstract
To test the hypothesis that an increased cAMP concentration improves skeletal muscle force development, we stimulated mouse soleus and extensor digitorum longus (EDL) in the presence of isoproterenol (1 × 105 mol·L1), a β-adrenergic agonist, or N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dcAMP) (1 × 103 mol·L1), a membrane-permeable cAMP analogue. Drugs used in the challenges were dissolved in KrebsHenseleit bicarbonate buffer (Krebs) at 27 °C and gassed with 95% O2 5% CO2. Stimulation at 50 impulses·s1 for 0.5 s produced an isometric tetanic contraction. Over 25 min of contractions at 0.6 contractions·min1, developed force increased significantly with the addition of isoproterenol (soleus, 2.5% ± 1.1%; EDL, 13.8% ± 2.0%) or dcAMP (soleus, 2.3% ± 0.5%; EDL, 10.9% ± 1.9%) as compared with vehicle controls (cont) with Krebs added (soleus, 0.0% ± 0.2%; EDL, 2.5% ± 0.7%). To investigate the role of Ca2+ availability, we amplified or attenuated sarcolemmal L-type Ca2+ channels with Bay K 8644 (Bay K) (5.6 × 106 mol·L1) or diltiazem hydrochloride (dilt) (104 mol·L1), respectively. Ca2+ release from the sarcoplasmic reticulum was increased with caffeine (2 × 103 mol·L1) or decreased with dantrolene sodium (dant) (4.2 × 107 mol·L1). With Ca2+availability modified, dcAMP addition in soleus significantly increased force development above control (cont, 2.3% ± 0.4%; Bay K, 4.0% ± 1.0%; dilt, 52.3% ± 3.6%; caffeine, 2.3% ± 0.7%; dant, 6.0% ± 2.0%; dilt + dant, 55.0% ± 23.0%). In EDL, the addition of dcAMP also increased force development above control (cont, 13.7% ± 1.9%; Bay K, 17.0% ± 4.0%; dilt, 170.0% ± 40.0%; caffeine, 23.0% ± 4.0%; dant, 72.0% ± 10.0%; dilt + dant, 54.0% ± 14.0%). Thus, a positive inotropic effect of cAMP existed in both fast- and slow-twitch mammalian skeletal muscle with both normal and altered Ca2+ flux into the sarcoplasm.Key words: skeletal muscle contractility, L-type Ca2+ channels, Ca2+ flux from sarcoplasmic reticulum, fast- and slow-twitch skeletal muscle, isometric tetanic contractions.
Publisher
Canadian Science Publishing
Subject
Physiology (medical),Pharmacology,General Medicine,Physiology
Cited by
7 articles.
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