CONTRACTION AND DEPOLARIZATION-INDUCED BY FETAL BOVINE SERUM IN AIRWAY SMOOTH-MUSCLE

We investigated the effects of fetal bovine serum (FBS) on the resting membrane potential and muscle tone of canine airway smooth muscles us ing tension recording and microelectrode methods. At concentrations > 0.1%, FBS induced a sustained increase in muscle tone. At concentratio ns > 1%, FBS depolarized the resting membrane potential of dog trachea in a dose-dependent manner. When FBS was dialyzed, it failed to induc e a sustained increase in muscle tone or to depolarize the membrane, i ndicating that FBS contained factor(s) that induced contraction of dog airway smooth muscles. When FBS was dialyzed against distilled water, the outer solution which was freeze dried and then reconstituted (> 1 % in original vol) induced a sustained increase in muscle tone, indica ting that FBS contained dialyzable factor(s) that increased muscle ton e and depolarized the resting membrane potential of dog airway smooth muscles. Methysergide (10(-6) M) or cyproheptadine (10(-6) M), nonspec ific antagonists to serotonin receptors, 5-hydroxytryptamines (5-HT1 a nd 5-HT2), markedly reduced the FBS-induced increase in the muscle ton e to similar to 20% of the original value but did not abolish the resp onse. On the other hand, methysergide (10(-6) M) completely suppressed the increase in the muscle tone evoked by peak fractions obtained by application of the dialysate of FBS or 5-HT to a Cls reverse-phase col umn, indicating the peak fractions contained only 5-HT. These observat ions indicate that FBS contained 5-HT and an unknown factor(s) respons ible for increase in the muscle tone of the airway smooth muscle induc ed by FBS.