Despite the relative stability of the extracellular space of healthy higher vertebrates, mammalian cell

volume homeostasis is constantly challenged by intracellular dynamics, pathological events or the

migration of cells between environments of varying osmotic strength. To counter the effects of volume

perturbations evolution have developed system of channels and transporters to tightly control volume

homeostasis.

In the past decades evidence has been mounting, that the importance of these volume regulated channels

and transporters are not restricted to the defense of cellular volume but are also essential for a number of

physiological processes such as proliferation, controlled cell death, migration and endocrinology.

The thesis have been focusing on two Channels, namely the swelling activated Cl- channel (ICl, swell) and the

transient receptor potential Vanilloid (TRPV4) channel.

I: Cl- serves a multitude of functions in the mammalian cell, regulating the membrane potential (Em), cell

volume, protein activity and the driving force for facilitated transporters giving Cl- and Cl- channels a major

potential of regulating cellular function. These functions include control of the cell cycle, controlled cell

death and cellular migration. Volume regulatory mechanisms has long been in focus for regulating cellular

proliferation and my thesis work have been focusing on the role of Cl- channels in proliferation with specific

emphasis on ICl, swell. Pharmacological blockage of the ubiquitously expressed ICl, swell will decrease

proliferation in several cell types, including Ehrlich cells. A differentiated expression of ICl, swell in the cell

cycle has been described in different cell types indicating a regulating role. In Ehrlich Lettré ascites (ELA)

cells we suggest the differentiated expression of ICl, swell to be protective rather than regulating, while the

role of Cl- in proliferation is due to other Cl- channels regulating Em.

II: The volume regulated response to hypotonic stimuli is Ca2+ dependent in the majority of endothelial cells.

TRPV4, a member of the Transient Receptor Potential (TRP) channel family is a Ca2+ permeable nonselective

cation channel, which is activated by cell swelling. Besides cell swelling, however, TRPV4 is also

activated by heat and a number of synthetic compounds. Despite of intense investigation of TRPV4, the

structure function relationship is still rudimentary understood. Potential agonist binding sites have been

proposed in transmembrane domains 3 and 4, in congruence with agonist binding sites of TRPV1. However,

the functional relationship between TRPV4 and agonist binding is not yet understood. In this thesis is

further elaborate the structure/function relationship between TRPV4 and its agonists. I identifies new

essential residues for agonist activation, which has the potential of explaining agonist gating in TRPV4. The

thesis will further complex the understanding of the TRPV4 pharmacore as new synthetic compounds are

identified to interact with TRPV4. Understanding the structure/function relationship of TRPV4 is essential

for future development of specific TRPV4 agonist for treatment of diseases causes by dysfunctional TRPV4.

E.g. two inherited bone dysplasias have recently been demonstrated in humans to originate from TRPV4

mutations.