RESUMO
The role of aging on contraction or relaxation through muscarinic or alpha-adrenergic receptors, respectively, was studied in isolated rat jejunum. Furthermore, the influence of extracellular calcium was analyzed, through functional and radioligand binding assays. The rank order of potency for selective muscarinic antagonists for M(1), M(2), and M(3) receptor subtypes, measured from affinity (pA(2)) values, was p-fluorohexahydrosiladifenidol (pFHHSiD) (M(3)) > pirenzepine (M(1)) > methoctramine (M(2)), indicating a predominance of M(3) subtype. This order was unchanged with age. Contractions by muscarinic agonist methacholine (MCh) were diminished in aged rats, resulting in lower apparent affinity (pD(2)) values, compared with adult controls. A larger decrease of MCh contractions occurred in aged rats after Ca(2+) withdrawal or after the calcium channel blocker isradipine. Changes were not detected for relaxation by adrenergic agonists. In conclusion, aging caused a decrease of MCh potency, which is probably related to the reduction of calcium sensitivity in jejunum.
Assuntos
Envelhecimento/fisiologia , Sinalização do Cálcio/fisiologia , Jejuno/fisiologia , Peristaltismo/fisiologia , Receptores Adrenérgicos alfa/fisiologia , Receptores Muscarínicos/fisiologia , Agonistas Adrenérgicos/farmacologia , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio Tipo L/efeitos dos fármacos , Diaminas/farmacologia , Isradipino/farmacologia , Masculino , Cloreto de Metacolina/farmacologia , Agonistas Muscarínicos/farmacologia , Antagonistas Muscarínicos/farmacologia , Piperidinas/farmacologia , Pirenzepina/farmacologia , Ratos , Ratos Wistar , Receptor Muscarínico M1/antagonistas & inibidores , Receptor Muscarínico M2/antagonistas & inibidores , Receptor Muscarínico M3/antagonistas & inibidores , Receptores Muscarínicos/efeitos dos fármacosRESUMO
In this study, we investigated the effect of aging on intracellular Ca2+ stores, as sarcoendoplasmic reticulum (SR) and mitochondria, and the influence of these compartments on contraction of rat colon smooth muscle [Bitar, K.N., 2003. Aging and neural control of the GI tract V. Aging and gastrointestinal smooth muscle: from signal transduction to contractile proteins. Am. J. Physiol. Gastrointest. Liver. Physiol. 284(1), G1-G7; Marijic, J., Li, Q.X., Song, M., Nishimaru, K., Stefani, E., Toro, L., 2001. Decreased expression of voltage-and Ca2+-activated K+ channels in coronary smooth muscle during aging. Circ. Res. 88, 210-234; Rubio, C., Moreno, A., Briones, A. Ivorra, M.D., D'Ocon, P., Vila, E., 2002. Alterations by age of calcium handling in rat resistance arteries. J. Cardiovasc. Pharmacol. 40(6), 832-840]. Calcium stores and contraction were evaluated by simultaneous measurements of fluorescence and tension in smooth muscle strips loaded with fura-2. Results showed that activation of muscarinic receptors by methylcholine (MCh, 10 microM), induced a greater contraction in aged rats than in adult animals. The inhibition of Ca2+ ATPase by thapsigargin (TG, 1 microM) did not prevent the refilling of SR either in adult or aged rats. MCh, in the presence of TG, induced an increase in transient fluorescence, indicating a release of Ca2+ from TG-insensitive compartment. The mitochondrial uncoupler, FCCP (5 microM), caused a greater increase in intracellular Ca2+ and tension in aged rats, indicating that mitochondria may accumulate more Ca2+ during aging. The present results show that changes in intracellular Ca2+ stores, such as mitochondria and SR, affect contraction and may cause dysfunctions during aging that could culminate in severe alterations of Ca2+ homeostasis and cell damage.
Assuntos
Envelhecimento/metabolismo , Cálcio/metabolismo , Colo/metabolismo , Contração Muscular/fisiologia , Músculo Liso/metabolismo , Envelhecimento/fisiologia , Animais , ATPases Transportadoras de Cálcio/antagonistas & inibidores , ATPases Transportadoras de Cálcio/fisiologia , Carbonil Cianeto p-Trifluormetoxifenil Hidrazona/farmacologia , Colina/análogos & derivados , Colina/farmacologia , Colo/efeitos dos fármacos , Colo/fisiologia , Interações Medicamentosas , Inibidores Enzimáticos/farmacologia , Feminino , Mitocôndrias Musculares/metabolismo , Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Músculo Liso/fisiologia , Ratos , Ratos Wistar , Retículo Sarcoplasmático/metabolismo , Tapsigargina/farmacologia , Técnicas de Cultura de Tecidos , Desacopladores/farmacologiaRESUMO
The effect of nantenine, an aporphine alkaloid isolated from Ocotea macrophylla H.B.K., was studied on contractions and Ca(2+) translocation induced by noradrenaline, Ca(2+), or K(+) in the isolated rat vas deferens from reserpinized animals. Concentration-response curves of calcium chloride (CaCl(2)) were performed in the vas deferens, in a Ca(2+)-free nutrient solution, using potassium chloride (KCl, 80 mM) as a depolarizing agent. In these conditions, nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly reduced the maximum contractions (E(max)) of Ca(2+) (IC(50)=2.6 x 10(-4) M) and noradrenaline (IC(50)=2.9 x 10(-4) M). The contractile responses were totally recovered after the withdrawal of nantenine. In addition, experiments performed to measure simultaneously the contraction and the increase of intracellular Ca(2+) induced by noradrenaline (10(-5) M) or KCl (80 mM) showed that nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly decreased both effects. The results suggest that a reversible block of Ca(2+) entry could be involved on the non-competitive-like antagonism of nantenine in rat vas deferens.