The invention provides variant venom peptides and polypeptides that specifically block potassium voltage gated ion channel Kv1.3. The invention also provides methods of inhibiting Kv1.3 channel activity, methods for treating disorders that are associated with undesired or aberrant Kv1.3 channel activity, methods for detecting Kv1.3 expression in target cells such as lymphocytes, and methods for diagnosing diseases or disorders that are associated with aberrant Kv1.3 overexpression.
