Antagonism frequency

In squid giant axons, PbTx causes a depolarization of the plasma membrane, repetitive discharges followed by depression of action potentials, and a complete blockade of excitability. This action is antagonized by TTX (83,84). PbTx depolarizes nerve terminals and induces neurotransmitter release (85,86) it depolarizes skeletal muscle cells (87) and increases the frequency of action potentials in crayfish nerve cord (88). PbTx also produces a contraction of the guinea pig ileum (89). All these effects are prevented by TTX. 

These data thus confirm our initial hypothesis that mGlu2/3 receptors are tonically active in lowering the level of brain arousal. Thus, antagonizing these receptors increases arousal as evidenced by the increase in waking and the stimulation of high-frequency EEG power. The striking increase in theta power was unexpected but is also consistent with increased arousal. 

In the rat, we observed a decrease of the spontaneous frequency of right atrial preparations and biphasic inotropic effects in left atrial preparations. Negative effects were not antagonized by atropine. The positive inotropic effect was modified very little by prior reserpinization or prior exposure to propranolol and phentolamine but was sensitive to Mn ions. On the other hand. 

Atropine, a tertiary amine, competitively antagonizes acetylcholine activity. Full therapeutic doses of atropine produce definite and prolonged inhibitory effects on the motor activity of the stomach, duodenum, jejunum, ileum, and colon, characterized by a decrease in tone and in amplitude and frequency of peristaltic contractions. 

Intakes of folic acid in excess of about 5,000 /xg per day antagonize the anticonvulsants used in treatment of epilepsy, leading to an increase in fit frequency (Section 10.9.6). 

The frequency and severity of the adverse effects of sulfonamides correspond to those seen with other antibacterial agents (2-5%). Dose-related effects, which tend to be more troublesome than serious, include gastrointestinal symptoms, headache, and drowsiness. Crystalluria can occur, but urinary obstruction is rare. Hematological adverse effects due to folic acid antagonism occur primarily in combination with trimethoprim. Hemolytic anemia occurs in patients with enzyme deficiencies and abnormal hemoglobins. Hypersensitivity... 

The specific Ca channel antagoni.sts verapamil, nifedipine, and diltiazem interact at specific sites on the calcium channel protein. These blockers do not occlude the channel physically but bind to sites in the channel, as they can promote both channel activation and antagonism. AITiniiy fix binding sites on the channel varies, depending un the status of the channel. The channel can exist in either an open (0. re.sting (R). or inactivated (I) state, and the equilibrium lx-, tween them is determined by stimulus frequency and mem-... 

Isocorydine was observed to significantly decrease the frequency of spontaneous contraction and muscle tension, but not the amplitude of contraction on the isolated isthmus of the oviduct of the rabbit The tension and frequency of spontaneous contraction was suppressed by the alkaloid at concentrations of 3-300 pmol/1, but the amplitude of contraction was decreased only at 300 pmol/1. The alkaloid antagonized the norepinephrine-induced contraction of the oviduct, and the transport of ova through the oviduct was delayed by isocorydine [285]. 

Recently Opmeer and Van Ree (33) have shown that the inhibition of the contractile response in the ileum which follows high-frequency stimulation and is presumably partially due to release of endogenous opiates (38) is also antagonized by increased Ca + concentrations. However, Opmeer and Van Ree also found that in vitro tolerance development was not affected when strips were incubated in Ca + free buffer containing EGTA. Thus it was proposed that although Ca + appears to be involved in the acute effects of opiates on the guinea pig ileum, it was much less important for In vitro tolerance development. 

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