Stromatoxin 1 is an inhibitor of Potassium Channel , a peptide which can be isolated from tarantulas. Stromatoxin 1 selectively inhibits K(V)2.1 , K(V)2.2 , K(V)4.2 , and K(V)2.1/9.3 channels. K(V)2.1 and K(V)2.2, but not K(V)4.2, channel subunits play a key role in opposing both myogenic and neurogenic urinary bladder smooth muscle (UBSM) contractions in rats.