Functional and molecular characterization of voltage-gated sodium channels in uteri from nonpregnant rats.
We investigated the function and expression of voltage-gated Na(+) channels (VGSC) in the uteri of nonpregnant rats using organ bath techniques, intracellular [Ca(2+)] fluorescence measurements, and RT-PCR. In longitudinally arranged whole-tissue uterine strips, veratridine, a VGSC activator, caused the rapid appearance of phasic contractions of irregular frequency and amplitude. After 50-60 min in the continuous presence of veratridine, rhythmic contractions of very regular frequency and slightly increasing amplitude occurred and were sustained for up to 12 h. Both the early and late components of the contractile response to veratridine were inhibited in a concentration-dependent manner by tetrodotoxin (TTX). In small strips dissected from the uterine longitudinal smooth muscle layer and loaded with Fura-2, veratridine also caused rhythmic contractions, accompanied by transient increases in [Ca(2+)](i), which were abolished by treatment with 0.1 microM TTX. Using end-point and real-time quantitative RT-PCR, we detected the presence of the VGSC alpha subunits Scn2a1, Scn3a, Scn5a, and Scn8a in the cDNA from longitudinal muscle. The mRNAs of the auxiliary beta subunits Scbn1b, Scbn2b, Scbn4b, and traces of Scn3b were also present. These data show for the first time that Scn2a1, Scn3a, Scn5a, and Scn8a, as well as all VGSC beta subunits are expressed in the longitudinal smooth muscle layer of the rat myometrium. In addition, our data show that TTX-sensitive VGSC are able to mediate phasic contractions maintained over long periods of time in the uteri of nonpregnant rats.
Instituto de Investigaciones Químicas, 41092 Sevilla, Spain.
Marian
M
Seda
Francisco M
FM
Pinto
Susan
S
Wray
Cristina G
CG
Cintado
Pedro
P
Noheda
Helmut
H
Buschmann
Luz
L
Candenas
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D062708:Epithelial Sodium Channel Agonists; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D062687:Sodium Channel Agonists; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D014599:Uterus / Q000187:drug effects / Q000502:physiology*; D014701:Veratridine / Q000494:pharmacology
D062708:Epithelial Sodium Channel Agonists; D053503:Epithelial Sodium Channels; D012333:RNA, Messenger; D062687:Sodium Channel Agonists; D015222:Sodium Channels; D014701:Veratridine; D002118:Calcium