Mechanisms mediating CCK-8S-induced contraction of proximal colon in guinea pigs.
OBJECTIVE
To investigate the effects of sulfated cholecystokinin octapeptide (CCK-8S) on the contractile activity of guinea-pig proximal colon.


METHODS
Proximal colonic smooth muscle (PCSM) strips were obtained from adult female guinea pigs and contractile response of PCSM strips was recorded using a polyphysiograph. PCSM cells were isolated by enzymatic digestion. Resting potential (RP), action potential (AP), large conductance potassium channel currents (I(BKCa)) and L-type calcium currents (I(Ca-L)) were recorded by patch-clamp techniques.


RESULTS
(1) CCK-8S (10(-7) mol/L) enhanced the mean contractile amplitude of colonic circular muscle and longitudinal muscle (LM) strips by 56.53% + or - 11.92% (P = 0.038) and 65.93% + or - 12.98% (P = 0.019), respectively, as well as the mean frequency of LM by 31.69% + or - 13.58% (P = 0.023), which were significantly attenuated by pretreating strips with devazepide, nifedipine, iberiotoxin, thapsigargin (TG) and BAPTA-AM (BA) respectively; (2) CCK-8S (10(-7) mol/L) increased the AP amplitude by 38.6% + or - 3.2% (P = 0.015), decreased AP duration by 36.9% + or - 8.7% (P = 0.026), and depolarized the RP from -61.3 + or - 2.7 mV to -29.8 + or - 5.9 mV (P = 0.032); and (3) Compared with the normal control group, CCK-8S (10(-7) mol/L) enhanced the peak current of I(BKCa) by 18.7% + or - 2.1% (from 916 + or - 183 pA to 1088 + or - 226 pA; at +60 mV; P = 0.029), which was inhibited by respective pretreatment with iberiotoxin and devazepide. Additionally, CCK-8S (10(-7) mol/L) intensified the peak current of I(Ca-L) by 40% (from 60 + or - 8 pA to 84 + or - 11 pA; at +10 mV; P = 0.012), compared to the normal control group, which was apparently suppressed by respective pretreatment with nifedipine, devazepide, TG and BA. In the respective presence of heparin and staurosporine, CCK-8S did not significantly enhance I(BKCa) and I(Ca-L).


CONCLUSIONS
The results suggest that CCK-8S promotes guinea-pig proximal colon contraction by CCK1 receptors, following activation of the inositol triphosphate-protein kinase C signal transduction pathway.
Zhu
Jie
J
Department of Gastroenterology, Renmin Hospital and Research Center of Structural Biology, Wuhan University, Wuhan 430060, Hubei Province, China.
Chen
Ling
L
Xia
Hong
H
Luo
He-Sheng
HS
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D003106:Colon / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D005769:Gastrointestinal Motility / Q000187:drug effects*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000378:metabolism; D049990:Membrane Transport Modulators / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D043886:Receptor, Cholecystokinin A / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D012844:Sincalide / Q000031:analogs & derivatives* / Q000494:pharmacology; D013997:Time Factors
C090019:8-sulfocholecystokinin octapeptide; D020746:Calcium Channels, L-Type; D005765:Gastrointestinal Agents; D051036:Large-Conductance Calcium-Activated Potassium Channels; D049990:Membrane Transport Modulators; D043886:Receptor, Cholecystokinin A; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D012844:Sincalide; D011188:Potassium; D002118:Calcium