Effects of serotonin on intracellular pH and contraction in vascular smooth muscle.
Serotonin (5-HT) and other contractile agonists stimulate Na(+)-H+ exchange in vascular smooth muscle. Since intracellular alkalinization, per se, stimulates contraction, we tested whether 5-HT-induced contraction was associated with an increased pHi. In HCO3(-)-free buffer (pHo 7.4), 5-HT (10(-5) M) increased pHi, as measured by 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence, from 7.10 +/- 0.03 to 7.34 +/- 0.03 (p < 0.01) in primary cultures of canine femoral artery vascular smooth muscle cells grown to confluence in the presence of 10% fetal calf serum. In HCO3- buffer (24 mM, pHo 7.4), resting pHi was 7.26 +/- 0.04 (p < 0.01 versus HCO3(-)-free buffer) but was not altered by 5-HT. In both types of buffer, 5-HT stimulated 5-(N-ethyl-N-isopropyl)amiloride-sensitive 22Na+ uptake (Na(+)-H+ exchange). In HCO3- buffer and in Na(+)- and HCO3(-)-free buffer, 5-HT increased 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive 36Cl- uptake, suggesting that 5-HT stimulated Na(+)-independent Cl(-)-HCO3- and Cl(-)-Cl- exchange activities, respectively. Individual vascular smooth muscle cells were then cultured on rat tail tendon collagen gels in the presence of 0.5% fetal calf serum, and cell length and pHi were measured by video and epifluorescence microscopy. 5-HT contracted cells in a dose-dependent, reversible, and ketanserin-inhibitable manner. These cells, like cells grown in 10% fetal calf serum, exhibited Na(+)-H+ and Na(+)-independent Cl(-)-HCO3- exchange. In HCO3- buffer, 5-HT contracted cells without an associated change in pHi. We concluded the following: 1) 5-HT stimulated both Na(+)-H+ and Na(+)-independent Cl(-)-HCO3- exchange activities in cultured vascular smooth muscle cells in parallel. 2) As a result of enhanced H+ and HCO3- efflux, pHi was not altered. 3) In the presence of HCO3-, 5-HT-induced contraction was not associated with a change in pHi.
Kahn
A M
AM
Department of Internal Medicine, University of Texas Medical School, Houston 77225.
Bishara
M
M
Cragoe
E J
EJ
Allen
J C
JC
Seidel
C L
CL
Navran
S S
SS
O'Neil
R G
RG
McCarty
N A
NA
Shelat
H
H
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D004285:Dogs; D005260:Female; D006531:HEPES / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013268:Stimulation, Chemical
D001639:Bicarbonates; D002712:Chlorides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012701:Serotonin; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D006531:HEPES; C039614:ethylisopropylamiloride