≤ -230 mV
||Hirsch RE, Lewis BD, Spalding EP, Sussman MR. A role for the AKT1 potassium channel in plant nutrition. Science. 1998 May 8 280(5365):918-21. p.919 middle column top paragraphPubMed ID9572739
|| Frans J. M. Maathuis, Dale Sanders, Energization of potassium uptake in Arabidopsis thaliana, Planta, August 1993, Volume 191, Issue 3, pp 302-307 link  Walker DJ, Leigh RA, Miller AJ. Potassium homeostasis in vacuolate plant cells. Proc Natl Acad Sci U S A. 1996 Sep 17 93(19):10510-4. PubMed ID11607707
||P.919 middle column top paragraph: "Also, using 80 mM as the cytoplasmic K+ concentration (primary sources) in the Nernst equation, it follows that a Vm [resting membrane potential] of at least -230 mV is required for K+ uptake to occur passively through a channel. Twenty percent of wild-type cells met this condition without making corrections for the fact that intracellular microelectrodes underestimate Vm (ref 16)." Primary sources  &  investigated Arabidopsis thaliana roots & barley (Hordeum vulgare L.) root cells, respectively.