Mesenchymal stem cells (MSCs) from bone marrow are believed to be an ideal cell source for cardiomyoplasty; however, cellular electrophysiology is not understood. The present study was designed to investigate ion channels in undifferentiated rat MSCs. It was found that three types of outward currents were present in rat MSCs, including a small portion of Ca(2+)-activated K(+) channel (I(KCa)) sensitive to inhibition by iberiotoxin and/or clotromazole, a delayed rectifier K(+) current (IK(DR)), and a transient outward K(+) current (I(to)). In addition, tetrodotoxin (TTX)-sensitive sodium current (I(Na.TTX)) and nifedipine-sensitive L-type Ca(2+) current (I(Ca.L)) were found in a small population of rat MSCs. Moreover, reverse transcription-polymerase chain reaction revealed the molecular evidence of mRNA for the functional ionic currents, including Slo and KCNN4 for I(KCa); Kv1.4 for I(to); Kv1.2 and Kv2.1 for IK(DR); SCN2a1 for I(Na.TTX); and CCHL2a for I(Ca.L). These results demonstrate for the first time that multiple functional ion channel currents (i.e., I(KCa), I(to), IK(DR), I(Na.TTX), and I(Ca.L)) are present in rat MSCs from bone marrow; however, physiological roles of these ion channels remain to be studied.