OUR RESEARCH OBJECTIVES
All of the cell functions are performed or supported by operation of channels (ion and water channels) and transporters (carriers and pumps) located on the membrane. The objectives of our division work are
1) to elucidate molecular mechanisms of most general cell activities, such as volume regulation, absorption/secretion and environmental signal reception,
2) to clarify roles of channels, transporters and receptors in these fundamental functions from the view-point of integrative biology, and
3) to throw the light on the relationship between these malfunctions and diseases or cell death, as well as 4) to study the multifunctionality of channel and transporter during cell functions or malfunctions.

The main subjects of our current research are as follows:
(1) "Molecular mechanisms of cell volume regulation and their physiological roles": Most cells regulate their cell volume even under anisotonic conditions. In the volume regulation mechanisms, a number of channels, transporters and receptors are involved (Fig. 1). We are investigating to identify volume-regulatory membrane machineries, including the volume-sensitive anion channel, and to clarify their physiological roles.

[RVI: regulatory volume increase, AVD: apoptotic volume decrease,
NVI: necrotic volume inclease]

(2) "Induction mechanisms of apoptotic, necrotic and ischemic cell death":
Dysfunction of cell volume regulation is associated with necrotic and apoptotic cell death (Fig. 2) which is coupled to persistent swelling (necrotic volume increase: NVI) and shrinkage (apoptotic volume decrease: AVD). Our aim is to pioneer the new field of 'PHYSIOLOGY OF CELL DEATH' through elucidation of the mechanisms of cell volume regulation and their dysfunction. We are attempting to focus our studies on the mechanisms of ischemic cell death of brain neurons and cardiac myocytes.

(3) "Mechanisms of multifunctionality of ion channels":
Channels are multifunctional proteins involved not only in ion transport and electric signal generation but also in sensors for environmental factors and regulators for other channels/transporters. We aim at discovering a new function of ion channels, elucidating the molecular mechanisms. CFTR and ATP channels are our current interest in this regard.

(4) "Mechanisms of secretion and absorption in gastrointestinal cells":
Activities of channels and transporters are prerequisites to functions in solute-absorbing enterocytes, Cl^--secreting enterocytes, gastric acid-secreting parietal cells, insulin-secreting β cells, and so on. We are investigating their roles.