This depends on the ionic model you are using. Following the standard nomenclature, the parameter should be called GK1 instead of g_K1: https://git.opencarp.org/openCARP/openCARP/-/blob/master/physics/limpet/models/README.md
You can look in the .model file in the source or use bench to learn about the available parameters for a specific model:
bench --imp=Courtemanche --imp-info
Ionic model:
------------
Metadata:
Authors: Courtemanche, M., Ramirez, R. J., and Nattel, S.
Year: 1998
Title: Ionic mechanisms underlying human atrial action potential properties: insights from a mathematical model
Journal: Am. J. Physiol. 275(1 Pt 2), H301-H321
DOI: 10.1152/ajpheart.1998.275.1.H301
Name: Courtemanche
Parameters:
ACh 1e-06
Cao 1.8
Cm 100
GACh 0
GCaL 0.1238
GK1 0.09
GKr 0.0294
GKs 0.129
GNa 7.8
GbCa 0.00113
GbNa 0.000674
Gto 0.1652
Ko 5.4
Nao 140
factorGKur 1
factorGrel 1
factorGtr 1
factorGup 1
factorhGate 0
factormGate 0
factoroaGate 0
factorxrGate 1
maxCaup 15
maxINaCa 1600
maxINaK 0.6
maxIpCa 0.275
maxIup 0.005
State variables:
Ca_rel
Ca_up
Cai
Ki
d
f
f_Ca
h
j
m
oa
oi
u
ua
ui
v
w
xr
xs