title: Differential actions of exogenous and intracellular spermine on contractile activity in smooth muscle of rat portal vein.
abstract: Effects of the naturally occurring polyamine spermine on electrical and contractile properties of the rat portal vein were studied. 1 mM spermine nearly abolished spike activity and spontaneous contractions and decreased the intracellular Ca2+ concentration ([Ca2+]i). The phasic force responses to 0.1 and 1 microM phenylephrine were partially inhibited, but not the sustain plateau contraction caused by 5 microM phenylephrine. The Ca(2+)-force relation in high-K+ (128 mM)-depolarized veins was shifted to the right, EC50 for Ca2+ increasing from 0.50 +/- 0.03 mM (control, n = 8) to 0.65 +/- 0.06 and to 0.94 +/- 0.03 at 1 (n = 4) and 10 (n = 3) mM spermine, respectively. However, at a Ca2+ concentration of 2.5 mM, giving maximal force, there was no effect of spermine (1 mM) on either force or [Ca2+]i. Whereas extracellular spermine thus reduced contractile activity at moderate levels of stimulation, increased intracellular concentration of spermine potentiated the force response to Ca2+. Intracellular loading of spermine by reversible permeabilization increased its concentration by 2-3 times. The spontaneous activity and response to phenylephrine were unchanged. However, the Ca(2+)-force relation of depolarized veins was shifted to the left, EC50 decreasing from 0.51 +/- 0.04 mM in controls (n = 7) to 0.36 +/- 0.02 mM in the loaded veins (n = 9). Spermine increased Ca(2+)-activated force in portal veins permeabilized with beta-escin. The degree of potentiation was consistent with observed effects in spermine-loaded intact veins. The results suggest that spermine at physiological intracellular concentration may contribute to the determination of Ca2+ sensitivity in vascular smooth muscle cells.
authors.affiliation: Department of Physiology and Biophysics, University of Lund, Sweden.
authors.forename: B O
authors.initials: BO
authors.lastname: Nilsson
authors.forename: M
authors.initials: M
authors.lastname: Gomez
authors.forename: R
authors.initials: R
authors.lastname: Santiago Carrilho
authors.forename: I
authors.initials: I
authors.lastname: Nordström
authors.forename: P
authors.initials: P
authors.lastname: Hellstrand
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D004594:Electrophysiology; D004928:Escin / Q000494:pharmacology; D005260:Female; D016257:Fura-2; D066298:In Vitro Techniques; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D011169:Portal Vein / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013096:Spermine / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D002120:Calcium Channel Agonists; D010656:Phenylephrine; D013096:Spermine; D004928:Escin; D002118:Calcium; D016257:Fura-2