Effects of local anesthetics and hemicholinium-3 on 45-Ca efflux in barnacle muscle fibers.
Benzocaine, which occurs in the uncharged form in the physiological range of pH, caused inhibition of 45-Ca efflux in branacle muscle fibers. By contrast, in the presence of a low external Ca-2+ concentration it produced stimulation of the efflux. Both the inhibitory and stimulatory actions of benzocaine appeared to be less potent than those of procaine. Hemicholinium-3 (HC-3), on the other hand, which exists only in the charged form, caused a large stimulation of the 45-Ca efflux following microinjection, and the potency of this action was found to be at least 10 times greater than that of procaine. External application of HC-3 produced inhibition occasionally. Effects of tetracaine were similar to those produced by procaine; however, its inhibitory action was greater in more alkaline solution, which is the opposite of that observed with procaine. Lidocaine produced a less consistent effect than procaine; the inhibitory action of the former was less potent but the stimulatory action of the two anesthetics were comparable, p-Aminobenzoic acid was without effect on 45-Ca efflux. These results indicate that both the charged and uncharged forms of local anesthetics are capable of causing stimulatory and inhibitory effects on 45-Ca efflux in barnacle muscle fibers, and that the inhibition produced is the result of action on the CA-Ca exchange system whereas the stimulation is the result of release of Ca from internal storage sites.
D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D003864:Depression, Chemical; D006426:Hemicholinium 3 / Q000494:pharmacology*; D066298:In Vitro Techniques; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D013268:Stimulation, Chemical; D001468:Thoracica / Q000378:metabolism*; D013997:Time Factors
D000779:Anesthetics, Local; D002132:Calcium Radioisotopes; D006426:Hemicholinium 3; D002118:Calcium