Kinetics of ATP-induced Ca2+ transients in cultured pig aortic smooth muscle cells depend on ATP concentration and stored Ca2+.
1. Single cultured pig aortic smooth muscle cells were studied using fura-2 and dual excitation wavelength microfluometry. 2. Extracellular ATP in micromolar concentrations induced a transient increase of [Ca2+]i due to Ca2+ release from internal stores. In the same concentration range application of ATP resulted in an increase of intracellular inositol phosphate level. 3. In a medium range of ATP concentrations (2-10 microM) the Ca2+ signal was oscillating, whereas at higher and lower concentrations only a Ca2+ transient with a single peak was elicited. 4. The rank order of potency for the tested purine and pyrimidine nucleotides was: UTP > ATP > ADP >> AMP = adenosine = alpha,beta-methylene ATP = 0. The response to the nucleotides could be abolished by the P2-purinoceptor antagonist suramin. 5. The latency between agonist application and onset of the Ca2+ transients as well as their amplitude and rate of rise are dependent on ATP concentration. 6. Removal of Ca2+ from the extracellular solution led to a progressive decrease of amplitude and prolonged latency of the Ca2+ transients. This shows that depletion of the Ca2+ stores affects kinetics of the ATP-induced Ca2+ release. 7. The inorganic Ca(2+)-influx blockers Ni2+ and Co2+ affected amplitude and latency in a manner similar to Ca2+ removal, while the Ca2+ antagonist nifedipine was ineffective up to a concentration of 10(-6) M. 8. These results reveal a dual dependency of the InsP3-induced Ca2+ release on agonist concentration and filling state of the Ca2+ stores, which supports the hypothesis of a feedback amplification between InsP3 and released Ca2+.
Kalthof
B
B
Institute for Cardiovascular and Arteriosclerosis Research, Bayer AG, Wuppertal, FRG.
Bechem
M
M
Flocke
K
K
Pott
L
L
Schramm
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000378:metabolism; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D005246:Feedback; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D011685:Purine Nucleotides / Q000494:pharmacology; D011742:Pyrimidine Nucleotides / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism; D013552:Swine
D011685:Purine Nucleotides; D011742:Pyrimidine Nucleotides; D018048:Receptors, Purinergic P2; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2